Background: HBV is the leading global cause of cirrhosis and primary liver cancer. However, the UK HBV population has not been well characterised, and estimates of UK HBV prevalence and/or incidence vary widely between sources. We aimed to i) extract and summarise existing national HBV prevalence estimates, ii) add a new estimate based on primary care data, and; iii) critique data sources from which estimates were derived.Methods: We undertook a narrative review, searching for national estimates of CHB case numbers in the UK  across a range of overlapping sources, including governmental body reports, publications from independent bodies  and articles in peer-reviewed scientific journals.  An alternative proxy for population prevalence was obtained via the UK antenatal screening programme which achieves over 95% coverage of pregnant women. We also searched for diagnoses of HBV in the QResearch primary care database based on laboratory tests and standardised coding.Results: We identified six CHB case number estimates, of which three reported information concerning population subgroups, including number of infected individuals across age, sex and ethnicity categories. Estimates among sources reporting prevalence varied from 0.27% to 0.73%, congruent with an estimated antenatal CHB prevalence of <0.5%. Our estimate, based on QResearch data, suggests a population prevalence of ~0.05%, reflecting a substantial underestimation based on primary care records.Discussion: Estimates varied by sources of error, bias and missingness, data linkage, and “blind spots” in HBV diagnoses testing/registration. The UK HBV burden is likely to be concentrated in vulnerable populations who may not be well represented in existing datasets including those experiencing socioeconomic deprivation and/or homelessness, ethnic minorities and people born in high-prevalence countries. This could lead to under- or over-estimation of population prevalence estimation. Multi-agency collaboration is required to fill evidence gaps. Nearly 300 million individuals worldwide are estimated to be living with chronic HBV (CHB) infection. Risks of complications and death are mitigated by screening to detect cases of infection, clinical monitoring of chronic infection (including liver cancer surveillance in high-risk cases), and antiviral therapy in those who meet treatment criteria.Hepatitis B virus (HBV) is the leading global cause of cirrhosis, and of primary liver cancer incidence and mortality. However, the attributable disease burden may be substantial in specific population subgroups including people who inject drugs, the prison population, people experiencing homelessness, and individuals belonging to minority ethnic groups and born in countries where the prevalence of CHB is higher. Thus, CHB is concentrated in potentially under-served, vulnerable and/or disadvantaged population subgroups.The United Kingdom (UK) is regarded as a low prevalence setting for CHB, as many CHB cases remain untested and therefore undiagnosed. Addressing the lack of HBV summary data in the UK would aid researchers and policy makers in addressing further evidence gaps.Epidemiological characterisation of the UK CHB population has been limited, with no central registry of infected persons. Existing data may primarily reflect new diagnoses (a combination of incident acute infection and new diagnoses of chronic infection), but caution is needed in making inferences about prevalence. Accurate estimation of prevalence is challenging, because complete HBV data are not likely to be well captured by large-scale electronic health record (EHR) databases for either primary or secondary care identifies specific goals, including diagnosis in 90% of chronic infections, 90% reduction in incidence of chronic infection, and 80% treatment coverage in those eligible. High quality epidemiological data are therefore crucial to focus and measure progress, inform policy and interventions, reduce inequities and underpin resource allocation. We therefore aimed to i) extract and summarise existing national HBV prevalence estimates; (ii) present new data from the QResearch primary care database; and iii) summarise and critique the data sources from which these estimates were derived.The World Health Organization (WHO) has set targets for viral hepatitis elimination within its Sustainable Development Goals for 2030. The Global Health Sector Strategy on Viral Hepatitis.We searched for estimates of CHB case numbers in the UK  across a range of available sources in a narrative (rather than systematic) review approach. We included UK-wide reports from government bodies, publications from independent bodies  and articles in peer-reviewed scientific journals, excluding smaller epidemiological studies when there was overlap of data sources with larger samples from other studies. We present positivity rates from each respective data source, but caution that these estimates are not representative of the true UK-wide population prevalence. Details of study samples/denominator are provided. The Office for National Statistics (ONS) provides UK population estimates as a point of reference for the overall denominator. QResearch was established in 2002 and contains anonymised individual-level patient EHR. Data are collected prospectively and are linked to hospital episode statistics (HES), National Cancer Registration Analysis Service (NCRAS) and ONS mortality data. QResearch ethics approval is with East Midlands-Derby Research Ethics Committee (reference 18/EM/0400).’We also generated a new prevalence estimate, utilising data from the UK primary care database QResearch, which contains over 35 million patient records from more than 1800 individual practices.We identified individuals in the QResearch (version 44) database who had a record of a diagnostic Systemised Nomenclature of Medicine (SNOMED)/Read or International Classification of Disease (ICD) code indicative of CHB, or who had a history of ≥1 hepatitis B surface antigen (HBsAg) or viral load (VL) measurement. From this sample we identified individuals between 01 January 1999 and 31 December 2019, age ≥18 years with CHB, defined as: i) record of a diagnostic SNOMED/Read code indicating CHB; or ii) record of a diagnostic ICD-9 or -10 code indicating CHB; and/or iii) Presence of HBsAg or VL on ≥2 recordings ≥6 months apart. The characteristics of HBV infection in the cases we identified are further described elsewhere, which is another UK primary care database containing EHRs for over 16 million patients. This previous investigation identified CHB individuals from patients registered in the database between 2000 and 2015.We have also drawn on findings from a similar investigation previously undertaken in the Clinical Practice Research Datalink (CPRD).This article can be found on medRxiv. Differences between sources highlights varied sources of error, bias and missingness, problems with data linkage, and substantial “blind spots” in consistent testing and registration of HBV diagnoses.UK data for CHB epidemiology are summarised in. This likely gives the best estimate of diagnosed prevalence among a tested population, but because it combines acute incident infections and new diagnoses of pre-existing chronic infection, incidence and prevalence cannot be disaggregated.As HBV is a notifiable disease in the UK, the UK Health Security Agency, UKHSA , has a comprehensive surveillance system for monitoring burden of CHB, by monitoring testing and diagnoses across the care pathway. This incorporates data from diagnoses through to outcomes,  using laboratory testing surveillance (sentinel surveillance of blood-borne virus (BBV) testing in primary and secondary care settings), new laboratory diagnoses, hospital activity datasets and registries . However, these data have not yet been combined and incorporated in a statistical model to estimate prevalence. Sentinel surveillance captures testing in community, primary care and secondary care settings across a network of laboratories covering approximately 40% of the general population of England, but this group are self-selected low-risk individuals who have undergone deferral discussions, and are predominantly UK born, and therefore are not representative of the general population, leading to an under-estimate of prevalence. No existing estimates factor in the undiagnosed burden, which represents the majority of people living with HBV infection (the WHO estimates that only 10.5% of people with CHB are aware of their infection status). Furthermore, the highest prevalence of CHB is in groups for whom provision of healthcare is inadequate, and/or access to healthcare is challenging , so overall there are still many gaps in the data, and it is most likely that estimates using primary care datasets considerably underestimate the true burden. There is a need for more evidence to delineate epidemiology in these populations.The majority of diagnostic data are generated through testing individuals with risk factors for HBV infection or evidence of liver disease, and among those accepting risk-based testing (as captured in laboratory testing surveillance) likely overestimates the overall population prevalence. Alternative estimates can be generated from screening blood donors. These individuals comprise a larger percentage of the London city population as compared to other regions in the UK, and therefore regional differences must be considered when deriving a population-wide prevalence estimate, which can be achieved through statistical models.Previous investigation has reported an increased burden of HBV infection in young, male, socioeconomically deprived individuals belonging to ethnic minorities within the UK. Over time, expansion of this programme should provide an additional valuable source of epidemiological data.Less biased estimates are achieved by non-targeted testing programmes such as universal antenatal screening. Opt-out screening of blood drawn from patients admitted to a selection of Emergency Departments (EDs) for HBV, HCV and HIV is being piloted across 34 sites across the UK, with new HBV diagnoses outnumbering HIV or HCV by >2:1 in the first 100 days, blood safety (transfusion/transplantation) and laboratory data generated by other services, while secondary care data are typically only reliable for the sub-population enrolled in consistent hospital follow-up. Poor data flow between diagnostic testing and EHR reflect a low clinical follow-up rate following a positive HBsAg test. This limited linkage to care reflects how services may not provide well for the CHB population, with gaps in referral pathways, inadequate communication and education (including translation services), and failures to deliver services to marginalised communities. Therefore, EHR databases offer the potential to characterise a subset of those infected with HBV, but do not currently generate a picture that is generalisable to the wider infected population, and cannot on their own be used to estimate prevalence.While UKHSA surveillance data may include some demographic characteristics , unless linked to other healthcare datasets, they typically lack more detailed clinical and demographic indicators  which are needed to characterise the infected population. In contrast, EHR databases (such as CPRD and QResearch) have the advantage of collecting relevant demographic and clinical metadata which are not captured by UKHSA. However, linkage across data sources is disaggregated, and thereby each EHR-based estimate misses a portion of the infected population. For example, primary care data may not reflect testing conducted in secondary care and human immunodeficiency virus (HIV) have recently been generated using multi-parameter evidence synthesis and back-calculation models. Similar modelling approaches to produce estimates of HBV incidence and prevalence in the UK are warranted. Enhanced investment is needed to support the establishment of national registries with robust centralised data linkage between sources including national laboratory surveillance systems of BBV testing and new diagnoses, and thus determine which population subgroups are bearing the majority of the HBV disease burden. This will inform prevalence modelling and provide an evidence base for delivery of appropriate resources and interventions, and to benchmark progress towards elimination targets.Prevalence estimates for Hepatitis C virus (HCV)QResearch ethics approval is with East Midlands-Derby Research Ethics Committee (reference 18/EM/0400). All concerns were addressed.Is the work clearly and accurately presented and does it cite the current literature?YesIf applicable, is the statistical analysis and its interpretation appropriate?Not applicableAre all the source data underlying the results available to ensure full reproducibility?No source data requiredIs the study design appropriate and is the work technically sound?PartlyAre the conclusions drawn adequately supported by the results?YesAre sufficient details of methods and analysis provided to allow replication by others?PartlyReviewer Expertise:HBV, HIV, STI, epidemiology, biostatisticsI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. The authors have addressed the salient comments.Is the work clearly and accurately presented and does it cite the current literature?PartlyIf applicable, is the statistical analysis and its interpretation appropriate?Not applicableAre all the source data underlying the results available to ensure full reproducibility?YesIs the study design appropriate and is the work technically sound?YesAre the conclusions drawn adequately supported by the results?PartlyAre sufficient details of methods and analysis provided to allow replication by others?YesReviewer Expertise:chronic hepatitis B infection, clinical liver diseaseI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. In their manuscript, Campbell et al describe the available sources used to estimate the case numbers of hepatitis B virus (HBV) in the United Kingdom, while highlighting the major gaps in understanding HBV epidemiology in the country. The details on the data sources retrieved are clear, along with their limitations. I found the discussion to be particularly helpful. Nevertheless, there are some issues worth addressing. I appreciate that this is a narrative review, yet the information on what was searched , in which locations  and when  is unclear. It would also be helpful to include some notion of which databases were included and excluded. For instance, it seems that many small epidemiological studies intended to find prevalence or incidence in very specific demographic populations could be missed (which could help address some of the gaps stated by the authors). Including this information would help guide the reader as to how the authors arrived at their selection. I also very much appreciate the summary box, which includes recommendations on how to achieve national CHB caseloads. But given the low prevalence of HBV and higher prevalence in specific key populations, would it make sense to aim for a national CHB caseload estimate? The aim of these recommendations should more reflect what the authors stated in their title, towards understanding the epidemiology of HBV in the United Kingdom. It would also be helpful to include a column in this box with the gap(s) in knowledge corresponding to the given recommendation, so the reader can identify the limitations of existing data (and hopefully avoid it in the future). Finally, it is unclear why prevalence estimates were given in the results, or even why this was examined in the first place if the aim was to discuss data sources to understand HBV epidemiology . I would suggest that the authors make it clear why this statistic was included, possibly by adding it as a secondary objective. Minor comments: - Abstract. “……” is ambiguous. Please clarify. - Abstract. “sources of error” refers to what exactly? This term could be deleted as it seems that bias was more the focal point of the discussion. - Abstract. Although I agree with the sentence, “Multi-parameter evidence … may be applicable to HBV.” – this does not really seem appropriate for the abstract (as the result backing this argument is missing in the Abstract). - Introduction. The information on ERH is probably more appropriate for the discussion. The third paragraph in the introduction should focus not only on the limited data, but also the lack of summary on HBV data in the UK. This information could be used to help policy makers understand what exactly are the gaps in knowledge. - Introduction. It should be stated clearly in the aims that this is a narrative review .Is the work clearly and accurately presented and does it cite the current literature?YesIf applicable, is the statistical analysis and its interpretation appropriate?Not applicableAre all the source data underlying the results available to ensure full reproducibility?No source data requiredIs the study design appropriate and is the work technically sound?PartlyAre the conclusions drawn adequately supported by the results?YesAre sufficient details of methods and analysis provided to allow replication by others?PartlyReviewer Expertise:HBV, HIV, STI, epidemiology, biostatisticsI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. The authors extensively reviewed the current data regarding the chronic hepatitis B epidemiology in the UK. The authors also acknowledged limitations on current data about chronic hepatitis B due to the limited source. Therefore, it requires a broad spectrum study to cover entire population to help guide public health policy and control transmittable disease. I have no further comment on this manuscript.Is the work clearly and accurately presented and does it cite the current literature?YesIf applicable, is the statistical analysis and its interpretation appropriate?YesAre all the source data underlying the results available to ensure full reproducibility?YesIs the study design appropriate and is the work technically sound?YesAre the conclusions drawn adequately supported by the results?YesAre sufficient details of methods and analysis provided to allow replication by others?YesReviewer Expertise:HepatologyI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. This is an extremely important piece of work to estimate the epidemiology of HBsAg+ seropositivity in the UK. The authors summarized data from 6 sources, leading to a crude estimate for HBsAg seropositivity ranging from 0.27-0.73%. The following points should be addressed to further enrich the scientific contents and provide some directions for further research: 1. Ongoing pilot programs of universal HBV testing at Emergency Departments are being conducted in some NHS Trusts, especially after the COVID-19 pandemic. Would there be any chance that updated data from these pilot programs might have been recently reported and can be included in this piece? 2. Regional differences within the country, or even to a smaller scale, within a city, should also be appreciated. For instance, East London is likely having a much higher prevalence of HBsAg+ than the West/ North side of the city. While population-based data is very important, targeting high-risk groups  is equally crucial to inform healthcare strategies such as resource allocation. This is also relevant to UK in view of the low overall prevalence of HBsAg , and population-based screening may not be as cost-effective as other highly endemic regions. Although the CDC has updated the recommendations since 2022 to screen for HBV infection for at least once in the lifetime for all adults, the actual implementation of such approach will highly depend on the resources available. Therefore, it would be helpful if there is data for HBsAg seroprevalence in the high-risk groups; and in addition to that addressed in this article , regions that are traditionally considered to be impoverished areas or known to harbour a relatively high proportion of immigrants, should be the target groups for such opportunistic approaches. 3. Would there be any overlap between the laboratory-identified HBsAg+ cases from UKHSA with other data sources?  4. Risk of bias and sampling error is well acknowledged – the authors may also include data from the NHS Blood and Transplant study published in Transfusion 2021 which reported a seroprevalence of HBsAg+ being 6.9/ 100,000 donors between 2009-2018.Is the work clearly and accurately presented and does it cite the current literature?PartlyIf applicable, is the statistical analysis and its interpretation appropriate?Not applicableAre all the source data underlying the results available to ensure full reproducibility?YesIs the study design appropriate and is the work technically sound?YesAre the conclusions drawn adequately supported by the results?PartlyAre sufficient details of methods and analysis provided to allow replication by others?YesReviewer Expertise:chronic hepatitis B infection, clinical liver diseaseI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.


As COVID-19 cases started to rise in early 2020 and hospitalisation rates increased, health systems began to postpone non-emergency (elective) procedures to keep capacity available for COVID-19 patients, and to avoid elective patients being infected. This has subsequently led to longer waiting lists and waiting times in virtually all countries. Issues around staff recruitment and retention, which have been exacerbated by the COVID-19 pandemic, have further aggravated the problem. For patients with common elective surgeries, such as hip and knee replacements, the backlog in care means that improvements in health and quality of life are postponed. For urgent care, such as missed chemotherapy sessions for cancer care, the delays can have more severe consequences. For other patients, the postponement of specialist appointments may lead to missed referrals for serious ailments. Increasingly also primary care has become affected leading to late diagnosis of chronic diseases, as well as inadequate follow up and control of these patients. Each delay in diagnosis and treatment may worsen health problems, prolong recovery and decrease the patients’ chances of survival. Countries are now left playing catch-up on these backlogs. There is however great uncertainty regarding the size of the backlogs, how much current and future capacity will be required to address them, and how much provider and workforce capacity will be needed for COVID-19 patients which will detract capacity for non-COVID patients. If health systems do not manage to reduce the backlog, they risk worsening health outcomes and wasting important health gains made in the last years. This workshop will discuss what we know about (1) the level of service disruptions and resulting backlog, (2) the drivers of backlog, and (3) which policies countries are using to address this. The workshop will conclude with an audience discussion about how to measure the true size of the backlog, the policy options for overcoming backlog and key priorities for further research.• The COVID-19 pandemic has led to substantial disruptions in care delivery leading to care backlogs in virtually all countries.• Countries have various policy options to tackle backlogs and bring down waiting times in the wake of the pandemic.


Neuronal regeneration in the central nervous system (CNS) is an important field of research with relevance to all types of neuronal injuries, including neurodegenerative diseases. The glial scar is a result of the astrocyte response to CNS injury. It is made up of many components creating a complex environment in which astrocytes play various key roles. The glial scar is heterogeneous, diverse and its composition depends upon the injury type and location. The heterogeneity of the glial scar observed in different situations of CNS damage and the consequent implications for axon regeneration have not been reviewed in depth. The gap in this knowledge will be addressed in this review which will also focus on our current understanding of central axonal regeneration and the molecular mechanisms involved. The multifactorial context of CNS regeneration is discussed, and we review newly identified roles for components previously thought to solely play an inhibitory role in central regeneration: astrocytes and p75NTR and discuss their potential and relevance for deciding therapeutic interventions. The article ends with a comprehensive review of promising new therapeutic targets identified for axonal regeneration in CNS and a discussion of novel ways of looking at therapeutic interventions for several brain diseases and injuries. The human brain harbors an array of unique capabilities not found anywhere else in the animal kingdom. It is undoubtedly the most advanced brain known of any living being. Thus, it is interesting to ponder why some capabilities intrinsic to less evolved animals that seem clearly beneficial for survival, such as regeneration, appear to be dramatically reduced in the human central nervous system (CNS) .Neurodegenerative diseases (ND), stroke, spinal cord injury (SCI) and traumatic brain injury (TBI) are just few examples for which it seems clear that, evolutionarily speaking, it would make sense to have retained some CNS regenerative capacity that simpler life forms possess . Upon injury, not only does the human CNS create a non-permissive environment for axonal regeneration through the formation of the glial scar , but alsNonetheless, studies attempting to restore function and structure to severed axonal processes in the CNS have been increasing over the years and it is clear there is a need for the development of such a therapy, given the broad spectrum of brain-related injuries and diseases that it could potentially impact on. Indeed, this topic has already been addressed by others , as haviIn order to gain insights into what is at play when we talk about axonal regeneration in the context of the CNS, first, one must have a clear picture of what regeneration of axonal processes involves in a context where its potential is higher and extensive regeneration is possible – the PNS.In the PNS nerve regeneration is widely observed. This can largely be attributed to the multitude of roles played by myelinating and non-myelinating Schwann cells. These cells are a driver and guiding force during development for axons of the periphery. Upon injury, Schwann cells undergo plasticity events that allow them not only to demyelinate the severed ends of an injured axon but also to potentiate regeneration by upregulating various pro-regenerative related genes and transcriptional mechanisms  .This is relevant because, apart from the reprograming that Schwann cells experience upon injury, they are capable of digesting myelin debris derived from injured axons and guide these severed processes through a non-permissive environment. Schwann cells transplanted into CNS injuries facilitate axon regeneration, although to a lesser extent than in the PNS because the extracellular space of injury in the CNS contains inhibitory components like myelin associated growth inhibiting proteins released by cells such as oligodendrocytes and the chondroitin sulfate proteoglycans (CSPGs). Additionally, repulsive axon guidance signals are expressed  which make it a much less axonal growth permissive environment than in the PNS . NeverthSchwann cells are not solely responsible for PNS regeneration, because there are other factors involved, but they do provide a bridge to guide axonal regeneration in the PNS. Also, Schwann cells behave in a stem cell-like manner, in the sense that they undergo a clear reprograming event, and through a combination of extracellular matrix (ECM) debris clearance and epigenetic alterations, act as the main facilitators of regeneration in the PNS .in vitro on both permissive and inhibitory substrates and was accompanied by activation of multiple regenerative signaling pathways implicating an important role for AMPK in regulating regeneration. The study also showed that the findings were replicated in vivo. Conditional deletion of AMPK prior to a dorsal column crush resulted in robust regeneration of sensory axons that entered and crossed the injury site. The results are promising and identify a new target for SCI therapy. However, the effects maybe specific to sensory neurons as AMPK activation via LKB1 produces a regenerative response in cortical neurons, suggesting distinct signaling pathways may be employed by different neuronal subtypes.A comparison of the response of central and peripheral branches of DRGs to axotomy also gives valuable insights into the mechanisms required to mount a successful regenerative response. In another study, the epigenetic events that follow PNS and CNS injury were investigated. Using RNAseq, ATAC, and ChIPseq to analyze epigenetic changes occurring following sciatic nerve axotomy (SNA) and dorsal column axotomy (DCA), it was reported that significant changes in epigenetic signature follow SNA but that the changes following DCA were different and more modest . They obin vivo following SNC with similar findings. Expression of the B domain resulted in significantly enhanced regeneration and this resulted in accelerated functional recovery as assessed by measurement of compound muscle action potentials. Immunoprecipitation studies showed that less of the Nrn-1 and Imp-β mRNAs co-precipitated with full length GBP-1 when the B domain was expressed, consistent with expression of this domain causing release of these mRNAs from the GBP-1. Indeed, transduction of constructs encoding the full length B domain or a peptide composed of amino acids 190–208 resulted in enhanced protein synthesis likely a result of disruption of GBP-1 function by the release of specific mRNAs. Interestingly, whilst Nrn-1 protein levels were increased the levels of Imp-β were not, suggesting that translation of Imp-β requires an additional signal. In summary, the authors have demonstrated a role for GBP-1 in the regulation of mRNA translation in DRG neurons. Moreover, they have shown that a fragment of the B domain of GBP-1 enhances protein synthesis and axon-outgrowth and thus is a potential therapeutic candidate for promoting regeneration in the CNS.In a different investigation The majority of previous studies on DRGs have used whole DRGs which has several drawbacks. First, they are composed of many cell types both neuronal and non-neuronal. Second, there are at least nine different neuronal subtypes present which perform different functions for example proprioceptors, nociceptors and pruriceptors. Lastly, not all the axons of the neurons present are axotimized following injury. A further complication is that cell dissociation procedures can act as injury signals. These studies were extended to identify the key drivers of the injury response. One day PI, several genes are upregulated including SOX11, ATF3, JUN, KLF6, KLF7, SMAD1, ETS2, and Bhlhe41. Of these ATF3 was the mostly highly expressed and its binding sites were most enriched in the induced RAGs. It was therefore selected for further study using ATF3 KO mice. They showed ATF3 KO mice exhibited delayed recovery after nerve crush and this correlated with lower expression of injury-associated genes at 1.5 and 7 days PI. Interestingly, the down regulation of the cell type specific genes was also attenuated in these mice suggesting an additional role for ATF-3 in this process. However, the authors suggest that this may be an indirect effect as there are no canonical ATF-3 binding sites present in the genes that determine neuronal specificity. It is of note that overexpression of ATF-3 in the CNS promotes regeneration and the hypothesis that regeneration may require expression of developmentally regulated TFs is not corroborated by this study.2 + wave that follows axotomy activates PKC which results in export of HDAC5 from the nucleus with consequent increase in histone acetylation and activation of a pro-regenerative program. ATF-3 is de methylated. In this study an additional method of ATF-3 activation is identified. They show that DNA breaks at the ATF-3 locus caused by DNA Topoisomerase I induce activation of ATF-3 and consequent induction of RAG gene expression. Moreover, they demonstrate that this effect can be accelerated by application of camptothecin, a topoisomerase1 inhibitor which results in the accumulation of more double stand DNA breaks as it prevents the religation of the nicked DNA. Injections of camptothecin resulted in accelerated expression of RAGs early after injury (18–24 h) which returned to normal compared to controls by 36 h. This was accompanied by increased neurite outgrowth of sensory neurons in vitro and enhanced regeneration following SNC in vivo. Thus, this topoisomerase inhibitor mimics the effect of a preconditioning lesion and is thus a potential therapeutic candidate for promoting PNS repair where a preconditioning lesion is not clinically applicable.In a follow up study Cheng and collaborators investigate the regulation of ATF-3 in more detail . There aCollectively, these studies have significantly advanced our knowledge of the mechanisms that take place when PNS neurons mount a regenerative response and have identified TFs and chromatin remodeling as key regulators of the process. These studies and others also give insights into the major barriers to regeneration . This wiin vitro and in vivo. This was demonstrated in two CNS injury models, optic nerve crush and SCI. Moreover, these negative effects of REST were only observed in the context of injury as deletion of REST had no effect in control uninjured animals or on DRGs plated on laminin as opposed to CSPGs. Thus the authors have shown that integrated genomics and bioinformatics can be a powerful method of identifying genes important for CNS regeneration. Uncovering a key master switch that regulates the expression of core RAGs is huge step forward in advancing our knowledge about how to boost the intrinsic ability of CNS neurons to regenerate.In a very recent study These beneficial regenerating roles of PNS Schwann cells are not present during CNS regeneration. In the CNS, apart from a lower capacity for protein transport, regeneration, microtubule density and axon diameter , the keyAfter injury to the CNS, be it traumatic, degenerative or ischemic, an anti-regenerative environment develops . This coThe formation of a mature glial scar after injury can be described as a sequence of three main events . First, Reactive astrocytes are key cellular players in the context of CNS injury, therefore its correct identification is essential. Although GFAP is a very used marker for astrocytes, there is accumulating evidence that GFAP expression may not serve as a sole marker of astrocyte reactivity as other cell types express considerable amounts of GFAP. GFAP overexpression by astrocytes does not entirely correlate with a specific reactive phenotype . A combiAfter glial scar maturation, at around the 2nd week post-injury, GFAP expression was described to decrease rapidly after a hippocampal stab wound injury (HSI) . This isThe previous point illustrates the heterogeneity of the glial scar, which depends on injury type and location and emphasizes the fact that one cannot make general assumptions that all glial scars will form and behave in the same way with regard to the extent to which they inhibit axon outgrowth and regeneration. However, the important role that astrocytes play following injury to the CNS seems to be common and undebatable.per se  it acts as a physical barrier for regenerating axons   . Nonetheb wound) .As previously mentioned, NG2+ glial cells, fibroblasts, pericytes and macrophages make up the cellular composition of the lesion core while the penumbra mostly consists of astrocytes and microglia. In order to gain insights into how to generate an environment more permissive for regeneration we need to take into account key events in glial scar formation and heterogeneity , namely N-cadherin whilst reactive astrocytes express β-catenin and metalloproteases (MMP2 and MMP13) consistent with their ability to migrate  cascades  pathway is considered a central signaling pathway for astrocyte generation . It has A neuro-inflammatory process forms an integral part of the CNS response to injury. Microglia release cytokines and inflammatory factors . This causes a response by reactive astrocytes to injury which can then become scar-forming astrocytes or not . ReactivThe inhibitory effects of CSPGs on axonal regeneration and plasticity are well documented. However, new roles for CSPGs concerning their involvement in neuro-inflammatory events have recently been unveiled. There is new evidence showing that they can regulate multiple aspects of the immune response in chronic inflammatory and demyelinating disorders of the CNS. In a new study by N-methyl-D-aspartic acid receptors (NMDAR), a-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors (AMPAR) and kainate receptors (KAR) (The term “excitotoxicity” refers to an overstimulation of NMDA receptor ionotropic glutamate receptors (iGluR), such as rs (KAR)  AMPAR anrs (KAR) . The overs (KAR) , causingThe decrease of glutamate reuptake mediated by the glial glutamate transporters is one of the proposed mechanisms to induce excitotoxicity . The EAA2+ increase, disturbing voltage dependent glial functions, and thus also increasing intracellular neuronal Ca2+, contributing to the overall excitotoxicity present in environments of large-scale cellular damage, such as the glial scar  expressed by neurons. This receptor forms a complex with the p75 neurotrophic receptor (p75NTR) and Lingo-1 . The p75Adding to the complexity of the signaling cascades which ensue following injury, the p75NTR is not only differentially expressed by myelinating glia, but it also seems to play different roles in determining regenerative outcomes in neurons and in glia. In Schwann cells (SC) for instance, p75NTR is only overexpressed following injury. As previously discussed, the capacity for the PNS to mount a regenerative response following nerve injury is superior to that of the CNS due to the role played by SCs. Transplantation of SC and olfactory ensheathing cells (OEC) markedly enhanced axonal regeneration in SCI models . It is lThe p75NTR can act as a neurotrophin receptor, transducing signals which trigger either nerve regeneration  or cell death  . HoweverIt is pertinent to remember that this is much similar to what seems to take place during CNS development, where astrocytes and radial glia function as guidance cells for neurons and a neurotrophin gradient guides axons to their target synapses . Some ofNeuroscientists in the field have attributed the regenerative failure of CNS neurons to both intrinsic and extrinsic barriers. Two classes of molecules present in the extracellular matrix have been shown to make a major contribution to inhibition of neurite outgrowth, the CSPGs and myelin associated glycoproteins (MAGs) present on CNS myelin. Following injury, CSPGs  are produced by reactive astrocytes, oligodendrocyte progenitor cells, macrophages and activated microglia (NG2 and versican) and are deposited in a glial scar . Early aReactive astrocytes play a key role in this process which is dependent on the STAT3 pathway. Supporting evidence for the involvement of the STAT3 signaling pathway in this process is that STAT3 knockout mice (KO) exhibit exacerbated damage and impaired recovery following SCI . ConversMyelin associated glycoproteins present in the scar are: NogoA, MAG, and OMgp, a GPI-linked glycoprotein . The myeAdult mammalian CNS neurons exhibit a markedly reduced capacity to regenerate. One cause is the downregulation of the mTOR signaling pathway which plays a role in neurite outgrowth. It is downregulated during development and the levels are further reduced following CNS injury . The impIn 2011, a ground-breaking study from the lab of Zhigang He  demonstrMoreover, researchers have demonstrated a role for PTEN in ChABC-mediated neurite outgrowth. PTEN mRNA and protein expression were significantly reduced in SH-SY5Y neurons expressing ChABC compared to GFP-transfected controls, and this was accompanied by the increase neurite length. In this study it is also shown that a similar increase in neurite length was produced by the PTEN inhibitor VO-OHpic . This isThe importance of the JAK/STAT pathway for neurite outgrowth of the corticospinal tract (CST) is supported by the observation that overexpression of STAT3, achieved by fusion with the viral activation domain VP16, enhanced neurite outgrowth of cultured primary cortical neurons  and consFurthermore, a study investigating genes involved in regeneration following optic nerve crush identified IL-22 as a key player in the process. They used shRNA knockdown and CRISPR gene editing to show that knockdown or inactivation of IL-22 resulted in the upregulation of two pro-regenerative signaling pathways; STAT3 and DLK, and this enhanced regeneration. The results support their hypothesis that reduced levels of functional IL-22 results in dis-inhibition of inflammation after nerve crush. This leads to increased levels of growth promoting transcription factors which in turn stimulate both STAT3 and DLK signaling pathways. This culminates in expression of regeneration associated genes (RAGs) and associated enhanced regeneration . SOCS3 iThis association between inflammation and nerve regeneration is also documented by Most studies have focused on knocking down molecules which inhibit intrinsic signaling pathways that promote axon-outgrowth, namely PTEN and SOCS3. However, others have taken the approach of boosting the activity of these pathways. Another way to activate mTOR is by activating the GTPase Rheb which acts upstream of mTOR. When constitutively active (ca–) Rheb was delivered to a ChABC-treated injury site of rats with SCI, together with a peripheral nerve graft (PNG), axons, mostly of propriospinal origin, grew out of the graft into the gray matter where there was evidence of synapse formation . In a laIn an innovative study by in vitro or in an optic nerve crush injury in vivo resulted in significant nerve regeneration  such as tau and MAP1B. These MAPs are more enriched on the labile domains extending into the distal region of growing axons , playingApart from what we have described, there are much more proteins with the role of modulating cytoskeleton dynamics and therefore constitute a promising target to promote axon regeneration following an injury. However, much more is to be discovered as this is a field that remains poorly understood and often neglected when considering regeneration of CNS axons in detriment for more cell/pathway directed therapeutic approaches. Rather, we would say that the overlap of some of the molecular pathways involved in regeneration discussed below with the impacts that CNS injury has on microtubule dynamics, described above, are a testament to the necessity to complement neuronal regenerative studies with microtubule dynamics analysis.Given both the number of processes occurring simultaneously and the heterogeneity of these events depending on injury severity and type , it is nIn a landmark study and as proof of principal, They report that propriospinal axons crossed the glial scar, lesion site and made functional connections with spared matter caudal to the lesion site. Interestingly, regeneration was further enhanced when a second dose of GDNF was delivered 1-week post-injury one segment caudal to the first site of delivery suggesting that spatial and temporal factors are important. Following the first dose of GDNF delivered to the first segment caudal to the injury site, axons grew in and around the hydrogel used for GDNF-delivery but not beyond. This is interesting because it is similar to the response of regenerating PNS neurons where constitutive expression of GDNF resulted in nerve entrapment whilst timed expression (1 month) resulted in successful regeneration . The AndIn another approach, transcription factors required for axon growth during development and down regulated in adult neurons or differentially expressed between the PNS and CNS have been used to promote regeneration following injury. Administration of antibodies to Nogo A following SCI have produced anatomical and functional recovery in both rats and macaques and are about to re-enter clinical trials . It is oThe sugar chains present on the CSPGs are thought to be responsible for much of their inhibitory effect on axon outgrowth  and targProteus Vulgaris and injections of the enzyme into spinal cord lesions results in anatomical and functional recovery in rats . These target the protein core components of the CSPGs. ADAMTS4 specifically targets CSPGs . When reAn alternative to CSPG removal is to target the downstream signaling pathways through which they act to block neurite outgrowth. The activation of RhoA has been targeted using cethrin a potent RhoA inhibitor. Lithium has been used to block GSK-3β. The dose of lithium is an important factor determining outcomes because low doses promote axon outgrowth whilst higher doses are inhibitory. The results obtained in preclinical studies were encouraging but the outcomes in clinical trials to date have been disappointing. Other RhoA and GSK-3β inhibitors such as Ibuprofen are being assessed .There is accumulating evidence that non-coding RNA’s (ncRNAs) are dysregulated following CNS injury  promoted regeneration by lowering PTEN levels thus stimulating the mTOR signaling pathway. In another study the authors demonstrate that expression of miRNA-135s represses the expression of the transcription factor KLF4, a potent intrinsic repressor of axon regeneration in the optic nerve thereby promoting regeneration following a nerve crush. Additionally, another ncRNA, miRNA-30b has been shown to bind to the 3’end of Sema-3A mRNA (a potent inhibitor of regeneration in RGCs) blocking its ability to bind to its receptors thus preventing growth cone collapse. miRNA-21-5p has been shown to regulate fibrosis- related genes and it’s knockdown attenuates the formation of a fibrotic scar following SCI, one of the main obstacles for axon regeneration . Thus, tC. elegans model (In yet another study two different injury models [optic nerve crush (ONC) and a DRG conditional injury models], were used to study the effects of Lin28a/b. Lin 28 regulates the expression of several genes, including the insulin-phosphati-dylinositol 3-kinase (PI3K). Thus, it has a direct effect on mammalian target of rapamycin (mTOR) signaling. Lin 28 is an evolutionarily conserved and converts somatic cells to (induced pluripotent stem cells) iPSCs. It additionally plays vital roles in determining body size and controls the onset of puberty. It also influences glucose metabolism, tissue regeneration and results in Akt activation and GSK3β inactivation . Its funns model , as wellns model . This lein vivo l in the DRG conditional lesion model. Curiously knock down of either Lin28a or b resulted in no change in regenerative capacity yet knockdown of both resulted in significant inhibition of axonal regeneration  via interaction with miRNA-124. GFAP which is downstream of STAT3 was also reduced. Encouragingly, these changes were accompanied by improvements in neurological function .The effect of microglia phenotype in attaining successful axon regeneration is also highlighted in another study. Neonatal mice were subjected to a nerve crush of the spinal cord. Successful regeneration occurred across a scar-free lesion site. This was not replicated when older mice were used or if neonatal microglia are deleted confirming a central role for microglia in the process. The authors show that, in contrast to adult microglia, neonatal microglia undergo transient activation then return to a state of homeostasis. They secrete fibronectin and its binding proteins which form a bridge across the lesion site. It is of interest to note here that the Anderson paper identified fibronectin as one of the substrates favoring axon-outgrowth across the lesion site . NeonataPTEN knockdown via shRNA, as discussed above, is effective at promoting regeneration of the CST. Moreover, PTEN knockdown is still effective at promoting growth of CST axons 1 year post-injury (T8 crush) and thus may be a potential treatment for chronic SCI .de novo cell growth and abrogates activity-dependent immediate early gene induction and therefore may have adverse side effects, including preventing the formation of appropriate synapses required for functional recovery . The retroviral injection itself served as the stab injury. In this study the authors demonstrated that they were able to convert GFAP expressing cells into functional glutamatergic neurons (VGlut1 positive) expressing both NeuN and Tuj1 . They then proceeded to convert NG2 + glia into neurons and succeeded in generating both glutamatergic and GABAergic (GAD67 positive) neurons. They then moved on to try and convert glial cells into fully functional neurons in a more challenging model, a 5xFAD Alzheimer’s disease aged mouse model. Not only they were again successful in cell conversion but also demonstrated synaptic and dendritic activity (SV2 and MAP2 positive respectively) as well as NMDA, Ca2+, K+ and glutamatergic and GABAergic currents  have been used with great success. In one study neonatal (immature state) astrocytes were transplanted into a rat SCI lesion using collagen as a scaffold. The authors demonstrated that this resulted in improved spinal cord repair  and that this was accompanied by some functional improvements as evidenced by locomotor improvement . AnotherAs discussed earlier, the superior regenerative capacity of PNS neurons if largely due to the functions and properties of SCs. This inspired many studies using SC transplantation as a method to enhance regeneration in the CNS, mostly using SCI as an injury model and their potential for clinical applications has been accepted . RecentlThe glial scar represents a major barrier to regenerating axons as previously mentioned. Therefore, it seems clear that for a regenerative process to occur, we need to build an axonal guidance pool involving a combination of interventions to create the basis for the physical and molecular bridges required to move beyond this territory and to build on this foundation a means of promoting the re-stabilization of synaptic plasticity and function.While representing a considerable challenge, significant advances have been made in developing therapies that promote regeneration following CNS injury. The results from the studies documented above, give insights into which approaches will likely be needed to achieve successful regeneration. Although preclinical studies have given promising results, to date, no single intervention for SCI, stroke or traumatic brain injury has progressed from phase III clinical trials to gain MRHA/FDA approval. Thus, successful outcomes will likely require a combination of interventions. The studies described above have identified the major barriers to regeneration and potential therapeutic targets. The collective results suggest that an efficacious combined therapy will include at least four components: (1) a strategy to boost the intrinsic ability of a nerve cell to regenerate; (2) a strategy to counteract the inhibitory components of the glial scar; (3) a chemotactic cue to guide regenerating neurons to their correct synaptic targets; (4) include a form of rehabilitation. The studies described above suggest that the JAK/STAT and mTOR signaling pathways are promising targets for component 1. Component 2 could be achieved in several ways: (A) removal of CSPGs with ChABC and neutralization of myelin inhibitors with Nogo antibody; (B) blocking the downstream signaling pathways that mediate their action such as RhoA and GSK-3β, both of which can be blocked with Ibuprofen; (C) upregulating the production of regenerative substrates. An alternative approach is to provide a permissive surface across the lesion site via cellular transplants of NSC and/or immature astrocytes to create cellular bridges. Component 3 could be achieved by the delivery of neuron specific growth factors. This component will likely need to be tailored to the neuronal population in question. For instance, GDNF is chemotactic for propriospinal neurons  whilst NWith regard to the different alternatives for achieving component 2, a major strategy is using a degrading molecules of CSPG such as ChABC, either directly or in a viral vector transgene delivery. It is of note that preclinical studies have shown that ChABC exhibits synergy in almost all combination therapies tested and its actions do not overlap with any of them making it a desirable component of any therapy . ChABC aFuture research will be needed to determine the optimal timing, dose and duration of each intervention. ChABC can be used as an example of the importance of determining these parameters. (1) Timing: when ChABC is delivered before or at the time of SCI, the outcome is detrimental, most likely because CSPGs are beneficial shortly after injury . The besMoreover, the timing of the application of each component is also likely to be critical. In fact, when rehabilitation was initiated 1 day post-injury (SCI) and ChABC at 4 days post-injury, no improvements were observed but in a different study where ChABC was delivered acutely and rehabilitation initiated 1 week post-injury, significant improvements in hand function were reported . These rThe vast number of events which follow CNS injury emphasize the relevance of using a multi- pronged approach for achieving successful CNS regeneration. In terms of the constituents of such a multicomponent therapy, several candidates stand out as having the greatest potential. The potential of SC or SC-like cell, or more specifically glia, is well documented and their importance for regeneration can be inferred by the fact that they take part in the regenerative process in species where the central regenerative capacity is intact  and duriFuture studies should include a detailed characterization of the different cell types impacting the glial scar structure, of neural function, and particularly synaptic transmission and plasticity, and/or of animal behavior, which will constitute functional outcomes of the therapeutical strategies that will enable to distinguish between anatomical recovery alone from functional recovery. The assessment of each therapeutic intervention in several injury models is essential given the diversity of events following different injuries that depend on injury location, size, and type. The type of tissue damage that occurs following CNS injury is diverse, it can be due to degenerative disease, ischemia or traumatic injury. Besides the diversity associated to the pathology of these different types of tissue damage, any potential therapies will have one requirement in common: a method to enhance the regenerative capacity of the CNS. Hence, the potential impact of finding viable therapeutical strategies to improve central axonal regrowth after injury is of the utmost relevance. Targeting the inhibitory events preventing regeneration in the CNS, which might be epigenetic targets, cellular targets, or the pathways themselves may ultimately lead to a treatment (likely a combination of interventions) with far-reaching implications.The present review described and discussed not only the key knowledge obtained from decades of research but also the recent advances in the field of CNS regeneration. Among this knowledge are the cellular and molecular processes that are known to occur following an injury as well as relevant points when designing therapeutical interventions. However, there are still important gaps in our knowledge that have compromised the development of a successful strategy for CNS regeneration. The main gap is the reduced information regarding the sequence of events following an injury in the CNS and its vast heterogeneity. Considering the state of the art of nerve regeneration presented in this review, we hope the near future research will identify and characterize the missing building blocks necessary to construct a bridge of knowledge that will allow the passage to the other side of the glial scar.GC, FR, and AS wrote the manuscript. GC and FR designed the illustrations. EM and SV wrote, designed, and revised the manuscript. All authors contributed to the article and approved the submitted version.


Graphical Abstract Figure 1). Invasive assessment of MSNA to the point of single unit recordings with analysis of single postganglionic sympathetic firing, and hence SNA drive to the peripheral vasculature, is the gold standard for quantification of SNA in humans but is only available in a few centres worldwide because it is costly, time consuming and requires a high level of training. A broad picture of the underlying pathophysiological determinants of the increase in sympathetic outflow in COPD can only be determined if a combination of these tools are used. Various factors potentially determine SNA in COPD : Obstructive sleep apnoea (OSA) is highly prevalent in COPD, and leads to repeated bouts of upper airway obstructions with hypoxemia, causing repetitive arousals. This probably produces ongoing sympathoexcitation in the awake state, likely in the “blue bloater” phenotype, resulting in persistent vasoconstriction. Other variables likely describe a subset of COPD patients with increase of sympathetic drive to the heart, clinically likely in the “pink puffer” phenotype. Pharmacological treatment options of increased SNA in COPD could comprise beta blocker therapy. However, as opposed to systolic heart failure a similar beneficial effect of beta blocker therapy in COPD patients has not been shown. The point is made that although MSNA is undoubtedly increased in COPD (probably independently from concomitant cardiovascular disease), studies designed to determine clinical improvements during specific treatment will only be successful if they include adequate patient selection and translational state of the art assessment of SNA. This would ideally include intraneural recordings of MSNA and—as a future perspective—vagal nerve activity all of which should ideally be assessed both in the upright and in the supine position to also determine baroreflex function.This article explains the comprehensive state of the art assessment of sympathetic (SNA) and vagal nerve activity recordings in humans and highlights the precise mechanisms mediating increased SNA and its corresponding presumed clinical determinants and therapeutic potential in the context of chronic obstructive pulmonary disease (COPD). It is known that patients with COPD exhibit increased muscle sympathetic nerve activity (MSNA), as measured directly using intraneural microelectrodes—the gold standard for evaluation of sympathetic outflow. However, the underlying physiological mechanisms responsible for the sympathoexcitation in COPD and its clinical relevance are less well understood. This may be related to the absence of a systematic approach to measure the increase in sympathetic activity and the lack of a comprehensive approach to assess the underlying mechanisms by which MSNA increases. The nature of sympathoexcitation can be dissected by distinguishing the heart rate increasing properties (heart rate and blood pressure variability) from the vasoconstrictive drive to the peripheral vasculature (measurement of catecholamines and MSNA) ( Chronic obstructive pulmonary disease (COPD) is a disease characterised by chronic airflow limitation, especially in expiration. Obstruction and hyperinflation alongside systemic inflammation burden the respiratory muscles, especially the diaphragm, which may lead to chronic ventilatory insufficiency with first nocturnal, and later daytime, hypercapnia throughout the disease course . HoweverAccording to global prevalence estimates, approximately 9% of men and 6% of women have COPD, making it one of the most prevalent diseases worldwide, and the incidence of COPD is expected to increase further based on population demographics. In both COPD phenotypes, particularly in cases showing overlapping features, the disease has a significant impact and is one of the major causes of death in the developed world .Strategies to improve the overall prognosis of patients with COPD are therefore highly desirable. However, although guideline-based therapy with inhaled beta-agonists and anticholinergics improves functional status (and hence the daily symptom burden) in many patients, this pharmacotherapy has not yet been shown to reduce mortality in patients with COPD . This maThere are several methods for assessing sympathetic nerve activity (SNA). Heart rate (HR) or blood pressure (BP) variability  provide a more general indication of autonomic imbalance and of increases in the heart rate-increasing central drive properties of SNA in particular .On the other hand catecholamines and MSNA directly reflect the SNA axis and, as such, the peripheral drive to the vasculature (i.e. vasoconstriction) of the SNA axis which also explains lack of clear correlations between HRV, BPV and MSNA .In particular, MSNA recordings allow invasive real-time monitoring of the sympathetic burst rate within the efferent peroneal nerve, which provides a direct measure of SNA  Figure . This meLack of using a combination of the above mentioned methods in a large enough cohort of patients represents a dilemma because there are methodological limitations if only single metrics of SNA are used. Indeed, using a multimodal approach insights can be generated that facilitate understanding of the nature of increased SNA  in any disease. This also facilitates understanding of the pathophysiological mode of action necessary for any pharmacotherapy to be successful in attacking on increased SNA in various diseases as part of modern precision medicine.Increased SNA in COPD has been documented using all the above methods . The resIndeed, several studies have documented an increase in MSNA in COPD  Table 1Table 1. Graphical Abstract Figure 1).However, in COPD the background to increased MSNA likely is multifactorial and therefore deserves a multimodal approach to phenotype  and eventually understand it  concomitant cardiovascular disease .Single-unit recordings, which provide richer information than standard multi-unit recordings of MSNA, have revealed that there is increase in central sympathetic drive in COPD as demonstrated in 18 COPD patients . Unlike A multi-unit recording (including explanations to its measurement) of MSNA from a patient with COPD is shown in To the best of our knowledge, the SNA axis has not yet been studied in COPD using a combination of the above mentioned methods in a large enough cohort of patients making it impossible to determine the extent and nature plus the clinical mechanisms and phenotypes responsible for the increase in SNA in COPD to date. In fact, the cohorts of patients in whom MSNA was measured never exceeded 18 COPD patients, a multimodal approach of SNA assessment comprising catecholamines, heart rate and blood pressure variability and MSNA combined has never been applied and MSNA has not yet been put into the context of distinct clinical and physiological phenotypes of COPD patients , increased levels of systemic inflammation all as reviewed later in this review).Cardiovascular diseases and systolic heart failure (HF) in particular, is a disease in which the relationship between increased sympathetic activity and poor clinical outcomes, and as a therapeutic target, has long been established . Indeed,Mechanisms for the sympathoexcitation differ in each of these pathophysiological states and are generally still not completely understood, but it is clear that the increase in sympathetic outflow is not limited to the muscle vascular bed but affects many organ systems . For exaTherefore, currently recommended therapies for HF target elevated sympathetic outflow . Many ofDespite several previous observations, the underlying mechanisms for the sympathoexcitation seen in COPD and their relationship with concomitant cardiovascular disease are not completely clear. It is known that sustained hypoxaemia (as seen in COPD) causes a long-lasting increase in MSNA and blood pressure, and that this persists even following the return to normoxia .Primary lung damage per se, as seen in COPD, also increases plasma catecholamines, irrespective of concomitant cardiovascular disease, suggesting a general increase in sympathetic outflow . ConsecuTherefore, increased SNA in COPD could explain why patients with COPD are almost three times more likely to die of HF than smokers not diagnosed with COPD . Such daObstructive sleep apnoea (OSA) might be one of the most significant determinants of increased MSNA in COPD. Coexisting COPD and OSA is now commonly referred to as “COPD-OSA overlap syndrome” . It is eDespite this, little research has been conducted on the COPD-OSA overlap syndrome .The coexistence of COPD and OSA could be associated with particularly high sympathetic outflow, manifested as increased vasoconstriction, that would persist even in the awake state and can be reversed by nocturnal use of continuous positive airway pressure:This rationale is supported by three arguments.First, OSA is associated with cyclic oxygen desaturations, and it is known that—as noted above—cyclic hypoxaemia causes a sustained increase in MSNA and BP that persists even after the return to normoxia .Second, it is also known that episodes of airway obstruction during sleep  cause an increase in MSNA even under normoxic conditions and that this increase also persists in the awake state, leading, in the long term, to the development of arterial hypertension .Third, OSA is known to have unfavourable effects on sleep architecture, decreasing objective sleep quality and the time spent in deep sleep, all of which adversely impacts on nocturnal MSNA, as recently shown by our group . AlteratCuriously, the clinical phenotype in which such a marked sympathoexcitation with predominantly increased vasoconstriction due to OSA could be encountered, likely corresponds to the phenotype of the “blue bloater” rather than the “pink puffer”, a hypothesis that could be investigated in future experiments.Despite being an obstructive lung disease, metrics reflecting inspiratory muscle dysfunction rather than the actual extent of obstruction show the closest association with hypercapnic ventilatory failure in COPD. Inspiratory muscle dysfunction with hypercapnic ventilatory failure in COPD may contribute to an additional increase in sympathetic outflow, but this question has not been addressed to date. In fact, only one recent study showed that maximal inspiratory mouth occlusion pressure (PIMax) is inversely correlated with sympathetic outflow, manifested as a presumed increase in central drive to the heart, as assessed indirectly by heart rate variability, in COPD . In lineHowever, in this study neither inspiratory muscle dysfunction nor MSNA have been directly assessed using gold standard techniques. These would have comprised invasive measurement of the transdiaphragmatic pressure response to supramaximal magnetic cervical phrenic nerve stimulation (CMS) by double balloon catheters and invasive measurement of MSNA by microneurography. Combined application of PIMax, diaphragm ultrasound-derived metrics and cervical phrenic nerve stimulation-derived metrics provides a comprehensive pathophysiological picture of inspiratory muscle function, as evaluated and applied by our group .Clinically, once inspiratory muscle dysfunction is severe enough to result in muscle pump failure, it likely causes nocturnal hypercapnia that then might extend into the awake state in COPD, predisposing to precapillary pulmonary hypertension.Precapillary PH might develop in COPD, especially in those with advanced disease and respiratory insufficiency with chronic hypoxemia and/or daytime hypercapnia . PH probThis, and additional cardiac function and haemodynamic variables, can be assessed using state-of-the-art comprehensive transthoracic echocardiography, combined with a non-invasive hemodynamic monitor, as recently established by our group . HoweverIn this context, a comprehensive protocol for ultrasound of the diaphragm (the key inspiratory muscle) has recently been established by our group and applied to patients with precapillary PH levels of differing severity based on the 6-min walking distance (6MWD) .Systemic inflammation has been reported to be present in COPD, as shown by increased levels of circulating interleukin (IL)-1 beta, IL-6, tumour necrosis factor-alpha (TNF-α), high-sensitivity C-reactive protein (CRP) and total white blood cell count . Levels Systemic inflammation may have an additive effect on the increase in sympathetic outflow in COPD. Proinflammatory mediators like IL-6 and TNF-α may directly influence inspiratory muscle function, as shown in animal studies . Given tCertainly, given the evidence for an increase in plasma noradrenaline , MSNA and “sympathovagal” imbalance in COPD, there is a rationale for pursuing pharmacological means of reducing sympathoexcitation in COPD, such as through the administration of ß1-blockers to protect the heart . HoweverNew England Journal of Medicine recently reported the results of the first large prospective randomised placebo-controlled trial investigating the effects of a ß-blocker on exacerbations in patients with COPD  characterised by an increase in central drive to the heart, and not just as an increase in MSNA and peripheral vasoconstriction. Curiously, clinically that would likely correspond to the “pink puffer” without OSA and hence predominantly peripheral vasoconstriction, rather than the “blue bloater” phenotype.Thus, using a comprehensive, multimodal approach and state-of-the-art technology, future research projects must be designed to determine the extent and nature, plus the clinical mechanisms, responsible for the increase in sympathetic outflow in COPD, and their specific targets., inspiratory muscle dysfunction and systemic inflammation would then likely describe a COPD phenotype characterised by increased SNA manifesting an increased central drive to the heart. It is this subset of COPD patients (presumably without OSA) that needs to be specifically identified and enrolled as part of modern precision medicine trials in COPD as a crucial step towards achieving a therapeutic benefit of ß-blocker therapy on exacerbations in COPD.Based on pathophysiological considerations and a small number of previous studies, it can be hypothesised that in COPD patients without an established cardiovascular disease  it is concomitant OSA and poor sleep that is independently associated with increased SNA . Factors including PHWhile much discussion has been directed towards the sympathoexcitation seen in COPD, we should not forget that the primary neural control of airway diameter is achieved via the parasympathetic nervous system . AlthougIn COPD a new trial aims to selectively denervate parasympathetic supply to the airways . The poiRespiratory and cardiac modulation of multi-unit recordings of vagal activity has recently been quantified . With feCuriously, inappropriate sympathetic activation was shown to potentially upregulate IL-6 levels and vagal stimulation was suggested as a possible tool to reduce systemic inflammation, in a different pathological population characterized by increased sympathetic modulation—a “positive loop” that hence may also provide a potential novel treatment pathway in COPD .This will allow us to assess the firing properties of individual preganglionic parasympathetic axons directed to the airways, as well as to the heart, in the same way we have been able to record from single postganglionic sympathetic axons in awake humans .It is baroreflex-mediated modifications of the sympathetic drive that are responsible for the changes in heart rate, and they partially explain the link between MSNA and heart rate variations . Indeed,As far as heart rate variability analysis is concerned it should be kept in mind that the newer non-linear analyses  could be useful in these patients .We propose making parallel recordings from the cervical vagus nerve and from the common peroneal nerve when participants lay on a tilt table, and taking them from the horizontal to near-vertical position; we have success in obtaining stable recordings of muscle sympathetic nerve activity from the leg when tilting participants, and have no doubt about the stability of the vagus nerve recording during this challenge. This will help us, for the first time in humans, to answer the question as to how the firing properties of atrial receptors or baroreceptors from the aortic arch change with changes in gravitational load, how they change in hypertension and systolic heart failure and COPD and how they affect heart rate, blood pressure and sympathetic outflow to the muscle vascular bed.Little is currently known about the underlying pathophysiological mechanisms leading to the sympathoexcitation seen in COPD, especially in COPD-OSA overlap syndrome.Attempts to better understand these mechanisms require a multimodal, systematic approach to assess both the increase in sympathetic outflow, and to specific target organs, and the presumed underlying clinical mechanisms.A multimodal, systematic approach should comprise heart rate variability, blood pressure variability, plasma catecholamines and direct recordings of MSNA together to distinguish between differences in sympathetic outflow to the heart and to the muscle vascular bed. Furthermore, the presumed underlying clinical manifestations to assess are OSA and sleep, PH, inspiratory muscle dysfunction and systemic inflammation.Based on currently available scientific evidence, it likely is OSA with poor sleep that, in the presence of COPD, is independently associated with increased sympathetic Outflow. This is then associated with increased drive to the peripheral vasculature with vasoconstriction. Other clinical variables, namely PH, inspiratory muscle dysfunction and systemic inflammation, may describe additional phenotypes of COPD patients with increased sympathetic outflow to the heart.By phenotyping COPD patients with regard to the target organs affected by an increase in sympathetic outflow we might define a subgroup that can be enrolled in clinical trials to assess directed pharmacologic treatment. This would be a step towards modern precision medicine in COPD, and a crucial step towards determining the potential therapeutic benefit of ß-blockers on the rate of exacerbations in COPD.Finally, while much discussion has been directed towards the sympathoexcitation seen in COPD, we should not forget that the primary neural control of airway diameter is achieved via the parasympathetic nervous system. Only now are we invasively assessing the firing properties of individual preganglionic parasympathetic axons directed to the airways, as well as to the heart, in the same way we have been able to record from single postganglionic sympathetic axons in awake humans, more insights into which offer unprecedented future therapeutic potential in COPD.


Epilepsy is a multifaceted disorder that can have a variety of etiologic factors, including genetic and structural causes. Neuroimaging is an essential component of its diagnostic workup. Conventional MRI scans can reveal visible structural brain abnormalities that may be the cause of seizures in both common and rare forms of epilepsy. However, in some cases, even when the suspicion of an epileptogenic structural lesion is high, such as in patients being referred for epilepsy surgery, a conventional brain MRI may not reveal any abnormalities. Advanced neuroimaging techniques such as MRI fingerprinting, brain morphometry, functional MRI, and ultra-high field MRI can provide additional diagnostic information and can help identify subtle or cryptic lesions that may not be visible on a conventional brain MRI. This can aid in more accurate clinical assessments of individuals with epilepsy, or those with an unclear etiology. Advanced neuroimaging is a powerful tool to investigate neural networks underlying seizure generation, epilepsy-associated large-scale system reorganization, and substrates of cognitive comorbidities. Most advanced imaging techniques can be applied to study both groups and single subjects, providing working hypotheses that can subsequently be explored in larger studies. Comprehensive views can be further provided by multisite neuroimaging meta-analyses, that explore morphological and functional brain abnormalities shared by subjects with common epilepsies or specific syndromes.The aim of this Research Topic is to give an in-depth overview of the latest advances in epilepsy research that have been made using diverse and innovative neuroimaging techniques. Our focus has been 2-fold: (i) Hypothesis testing and pursuit of mechanisms: how advanced neuroimaging can be employed to verify or explore the pathophysiological processes underlying common epilepsies and (ii) Clinical application: to define the role of advanced neuroimaging techniques in the diagnostic workup of both common and rare epilepsies.via conventional neuroimaging approaches; investigation on the microscopic characteristics of brain lesions identified by conventional imaging; analysis of structural and functional brain abnormalities in specific syndromes or across the epilepsy spectrum; exploration of the functional networks associated with seizures/interictal spikes, epilepsy-related neural system reorganization, and cognitive comorbidities.With this purpose, we called for articles focusing on: identification of subtle morphological brain abnormalities Pizzanelli et al. proposed a functional connectivity study to investigate a group of adults with drug-sensitive temporal lobe epilepsy  by means of 3 Tesla resting-state functional MRI. They showed that reorganization of mesiotemporal functional connectivity can be observed also in seizure-free patients and that lateralization-related differences are remarkable. He et al. analyzed hippocampal malrotation with qualitative and quantitative parameters in adults with focal cortical dysplasia, disclosing no differences between patients and healthy controls. Zhang et al. explored brain morphometry of young patients with juvenile myoclonic epilepsy, showing widespread microscopic structural abnormalities associated with cognitive performances and disease course. Machegger et al. showed that quantitative analysis of diffusion restriction and ADC decrease on MRI is applicable to differentiate acute ischemic stroke from status epilepticus with high sensitivity and specificity. Lastly, Fukuma et al. developed a novel asymmetry method to localize areas of hyperperfusion in poststroke epilepsy using a single postictal single-photon emission computed tomography (SPECT) study. While the gold standard for localizing epileptogenic seizures in epilepsy is subtraction imaging of ictal and interictal perfusion SPECT coregistered to MRI (SISCOM), in many clinical settings, ictal perfusion studies are difficult to obtain, and postictal studies are used instead. Comparing a standardized asymmetry analysis vs. postictal—interictal subtraction of perfusion SPECT images, Fukuma et al. demonstrated that a single scan postictal SPECT asymmetry analysis may offer diagnostic results in certain cases, at the cost of a sensitivity reduced by 20%, which may be still complemented by the subtraction method in unclear cases. In certain clinical settings, such a stepwise procedure could result in reducing the number of scans needed for seizure focus localization, limiting radiation exposure, and scanning costs.Upon our call for papers, five high-quality manuscripts have been submitted and underwent peer-review. Three papers met the standards we deemed adequate for this topic and we gathered two additional articles of particular value. The quality of these selected articles was remarkable and allowed us to provide an overview on different and up-to-date techniques in advanced neuroimaging in epilepsy. One of the most relevant themes of this collection is the breadth of imaging-driven information that can be applied to categorize individuals with epilepsy. The widespread use of non-invasive biomarkers that might assist in predicting seizure outcome and associated comorbidities and to tailor epilepsy surgery would in fact be of utmost importance. We are confident that our community will strongly pursue this quest to improve the life and care of people with epilepsy.All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.


The rising burden of multiple chronic diseases requires countries to change the reactive approach of their health systems, originally designed to cure acute illness, to a proactive approach that scales up preventive interventions and integrates cure  and care . This requires a central coordination role for primary health care (PHC). PHC is the foundation for delivering health services to the population. It mainly encompasses the first level of professional health care and includes PHC practitioners and other health workers. Together, PHC providers can satisfy most curative and preventative health needs, ideally providing integrated services. In this way, PHC has the potential to agilely respond to population health needs; help individuals navigate their way to good health and stay healthy; prevent disease by identifying risk factors; and manage chronic disease outside of hospital settings. Yet PHC in many countries is not designed to fully realize these promises and ongoing reforms aim to strengthen it. Meanwhile, this potential was on display in several countries during the COVID-19 pandemic, when primary care doctors played a key role in making an early diagnosis; helping vulnerable people cope with their anxiety about the virus; reducing the demand for hospital services; and delivering vaccinations-all while reaching out to vulnerable patients and maintaining access to essential (non-COVID) services for the wider population using new in-person protocols or new digital solutions. This workshop will update the audience on recent PHC reforms across the EU and provide insights from three key examples-Estonia, Poland, and Slovenia. An introductory presentation sets the stage by putting PHC reforms in a wider context of reforms introduced across the 31 countries of the Health Systems and Policy Monitor network of the European Observatory on Health Systems and Policies between 2018 and 2021. A second presentation describes how Estonia has introduced a series of PHC reforms over time and used financial incentives to encourage multidisciplinary care. A third presentation looks to Poland, which from mid-2018 through 2021 piloted a multi-professional model of PHC organization in around 40 PHC practices, with an emphasis on care coordination and disease prevention. A final presentation highlights Slovenia, where a multidisciplinary, community-based, prevention-oriented service delivery model is being expanded to play a larger role in the prevention and management of chronic diseases as well as the country's COVID-19 response. The workshop concludes with an audience discussion on lessons learned from the three case studies and potential implications for other countries.• Strengthening primary health care is a key priority of many countries as they seek to improve integration of care.• Implementation of primary care reforms in shaped by the legacy of care delivery and requires a strong workforce, ongoing financial support, sustained policy focus, and collaborative governance.


The health and economic consequences of seasonal influenza present great costs to communities. Promoting voluntary uptake of the seasonal influenza vaccine among university students, particularly during the COVID-19 pandemic, can deliver protective effects for both individuals and the wider community. Vaccine uptake will be greatest when more of the social marketing benchmarks are applied. This systematic review summarizes evidence from programs aiming to increase seasonal influenza vaccination among university students. Six major electronic databases for health promotion studies  were searched in November 2021 to capture peer-reviewed studies reporting field trials that have sought to increase seasonal influenza vaccination in university student populations, without any restrictions regarding the publication period. Following PRISMA guidelines, this paper identified 12 peer-reviewed studies that were conducted in the field in the United States, Australia, and Spain. Three studies were targeted at healthcare students and the rest focused on wider university student populations. Studies were narratively summarized, evidence of social marketing principles were identified, and quantitative outcomes were meta-analyzed. The findings indicate that none of the field studies, even a self-classified social marketing study, had adopted all eight of the social marketing benchmarks in program design and implementation. The two studies that only used promotion, but not other marketing-mix and social marketing principles, reported increases in students’ intention to be vaccinated but not actual behavior. Given that change is more likely when more social benchmarks are applied, this paper identifies activities that can be included in flu vaccine programs to improve flu vaccine uptake rates. The analysis highlights a lack of field studies focusing on increasing rates of vaccination behavior as research outcomes in countries beyond the United States. Seasonal influenza  causes substantial morbidity and mortality in each winter influenza season. Prior to the outbreak of the COVID-19 pandemic, seasonal influenza killed about half a million people around the globe in 2018 [Although university students are a low-risk group for influenza complications and death, the highly contagious seasonal influenza still poses a severe health threat to university students and their close contacts. Seasonal influenza is a well-documented risk to university students , once inAccording to the World Health Organization (WHO) , vaccinaApart from the well-being of students, promoting seasonal influenza vaccination among university students could also deliver further protective effects for the community surrounding students. Whole communities can be protected from influenza viruses if a sufficiently high percentage of the population develop immunity to influenza . TherefoAlthough much research effort has been invested to understand the factors and barriers affecting university students’ attitudes and intentions to receive seasonal influenza vaccination ,11,12,13Human behavior is complex and factors leading to low vaccine uptake are diverse. Healthcare researchers, practitioners, and policymakers have been investigating approaches to motivate influenza vaccination among people who have high vaccine acceptance and to promote vaccination uptake among those who hesitate. People who have high vaccine hesitancy usually “delay in acceptance or refusal of vaccination despite availability of vaccination services” , imposinSocial marketing, among all approaches, has received a growing awareness among researchers for its effectiveness in addressing the issue of vaccine hesitancy ,20. The Social marketing is an evidence-based approach that has been applied effectively to promote global health ,24,25. SThe first benchmark criterion that a social marketing program has to fulfill is behavioral change, which requires that the intervention or program focus on delivering behavioral change within a fixed timeframe. The focus on behavior aims to ensure all efforts feature direct calls to action and extended program efforts beyond changing knowledge, attitude, or beliefs. The second benchmark, segmentation, distinguishes social marketing programs from other approaches. Social marketers who apply segmentation focus on identifying differences between people considering a range of demographic, geographic, psychological, or behavior characteristics  to ensurSocial marketing’s effectiveness as a behavior-change tool is widely established. Evidence indicates that behavior change is more likely when more of the social marketing benchmark principles are applied . The secSynthesize knowledge gained from previous seasonal influenza vaccination promotion programs or interventions that have effectively increased university students’ vaccination rates;Assess the extent to which social marketing principles were applied in identified studies;Inform healthcare policymakers and university management on the effective practices that can be applied to motivate university students to uptake annual seasonal influenza vaccines.This systematic review aims to:This systematic review followed the guidelines stated in the preferred reporting items for systematic review and meta-analyses (PRISMA), outlined by Liberati et al. .This study searched for possible related studies in six major electronic databases: PubMed, EBSCO, ProQuest, Ovid, Web of Science, and ScienceDirect. The following key terms were used:  AND ). The search was performed initially in April 2021 before the development of a campus-wide influenza vaccination campaign and an updated search was completed in November 2021. No restriction was set on the publication type, published time and language during the initial search.This review adopts the PICOS  approach in accordance with PRISMA guideline . The revIn addition, the following exclusion criteria governed which studies were not eligible for this systematic review: (1) studies including target groups who are not college or university students; (2) studies with mixed results for college or university students and other target groups, with no data presented separately; (3) studies in which vaccination behavior is not measured as an intervention outcome; (4) studies with co-administration of other vaccines; (5) studies without a control group or baseline comparison; (6) studies evaluating pandemic influenza vaccines only; (7) studies not published in English; or (8) studies not published in a peer-reviewed journal, thus grey literature was excluded from this paper. Articles that meet any one of the exclusion criteria were excluded immediately with no further inspection.After the search was performed in the six databases to identify previous publications meeting the selection criteria, duplicated results were removed before the screening process. Two reviewers then worked independently through the screening process in full compliance with the inclusion and exclusion criteria stated in This review attempted to identify the presence of social marketing principles. This was achieved through examining reported study elements and cross-checking reported information against the eight social marketing benchmark criteria. A coding framework based on existing definitions of social marketing  were useAll the 12 studies reported programs targeting seasonal influenza vaccination behavior. Although we did not limit the search results using publication date, all the 12 studies were published in the last 10 years . All studies reported interventions or programs implemented that aimed to increase the vaccination rate of seasonal influenza vaccines among college or university students. The intended behavior outcomes were measured in terms of influenza vaccination rate . This review intends to synthesize knowledge from previous studies applied in the field to explore the effectiveness of seasonal influenza vaccination programs. Given behavior change rates are greater when more of social marketing’s eight core principles are applied, this review assessed the extent to which social marketing benchmarks were present in studies aiming to increase vaccination rates. Of the 12 included studies, only one study  was selfAll nine studies ,50,51,52Although full-scale campus-wide or school-wide promotion programs were found to effectively increase flu vaccination rates among university students by as much as 131% , the absp-value of Shropshire et al.’s study is 0.345 (p > 0.05) and does include the null value, indicating that the outcome of the study is not statistically significant. The effect was strongest (most distant from 1.0) in the program conducted by Saro-Buendía et al. [p < 0.001). Influenza intervention program is better than control as the overall effect estimate, and its 95% confidence intervals are to the right of the line of no effect.Statistical analyses of the impact of vaccination promotion programs on the vaccination rates reported in the included studies was conducted using Comprehensive Meta-Analysis version 3 . Seven sa et al.  which usa et al.  used fiva et al.   or intangible  benefits as an exchange to motivate target segment(s) to engage voluntarily with the program . Four stIn a social marketing intervention program, the 4Ps of commercial marketing mix  should be used whenever the approaches are financially feasible . Table 4Product, in this systematic review, refers the advocated behavior of getting vaccinated . Since aPlace refers to where the vaccine is administered and ideally ensuring that a convenient location is made available to support students to obtain vaccinations  , communication channel strategy, and source strategy  . The useRoberto et al.’s study  that expIncreasing seasonal influenza vaccination rates among university students is an important public health agenda for campus communities and broader society. Research reporting solutions that deliver evidence-based approaches that can be applied to increase vaccine uptake are lacking. According to the PRISMA flowchart , most exHealth behavior is complex. As theories could provide an organizing framework to explain and predict behavior, the clear application of theory is expected to enhance intervention effectiveness . HoweverAmong all studies on vaccination behavior, there are only three RCTs in eligible studies. Thus, the internal validity is quite low in eligible studies and the effect size may be overestimated. Hence, more RCTs are required in future studies.Rundle-Thiele et al.  showcaseNone of the studies assessed in this review have conducted or referenced segmentation analysis to identify homogeneous groups sharing similar characteristics in the target population. The three studies ,51,52 foOnly three studies ,47,51 coAlthough four studies mentioned the use of theory underpinning program development, only Bronchetti et al.  delineatAccumulating evidence from social marketing indicates that programs should be designed with, and not for, target audiences . Only twElements of the marketing mix  should then be built based on insights from the co-create process to engage students in an exchange for voluntary vaccination behavior. Two studies  and place (convenient locations and hours) were found to be the most important components of an effective vaccination program. While monetary incentives deliver a strong nudge to vaccinate, non-monetary nudges have no effect. For promotion, students should be reached using multiple online and offline communication channels. While online channels such as a school website and email were found to be effective, the use of social media may not affect vaccination behavior. This finding echoes with the study of Benis et al.  which foThis paper is the first systematic literature review to synthesize extant knowledge in peer-reviewed journals of social marketing application in seasonal influenza vaccination interventions targeting university students, using the eight social marketing benchmark criteria. Although only one study self-identified as using social marketing, most programs that effectively increase influenza vaccination rates were found to adopt a full marketing-mix and a few other social marketing components. A lack of behavior change studies in countries beyond the USA is highlighted. Future studies that fully exploit the potential of social marketing in program design and implementation would enable policymakers and university healthcare promotion personnel to improve influenza vaccine uptake on university and college campuses. In particular, omission of segmentation, students’ active involvement in program planning and/or delivery, consideration of competition, formative research for insight generation, provision of incentives for exchange, and the lack of theory-driven program design were highlighted as areas for improvement that may be capable of yielding even higher vaccine uptake rates.Despite its contribution, this paper has several limitations. This review focused on university students and on-campus programs. Since students’ decision to receive influenza vaccine can also be influenced by off-campus factors from family members and friends, propaganda about vaccine in social media and other online platforms, community health support, personal health insurance, future research can explore a system-approach of program design to holistically influence vaccination behavior. For the meta-analysis, not all the selected studies were included because sample sizes were not provided in some studies. The treatment effects of intervention programs might vary across the studies although as different social marketing benchmarks and marketing mix were applied. In addition, those studies span across last decade. The mind-set of the people might change as time goes by. Lastly, this review did not include grey literature although relevant vaccination program learnings and evaluations can be found in the grey literature. Future research can consider synthesizing informal assessments reported in the grey literature to further benefit development of better influenza vaccination programs for students.