Introduction: TheWHO currently recommends giving pneumococcal conjugate vaccines (PCVs) as three doses – either three doses in infancy with Pentavalent vaccine (3p+0), or two doses in infancy followed by a booster around 12 months (2p+1). However, their high price is a barrier to introduction and sustainability in low and middle-income countries. We hypothesize that a schedule with a single priming and a booster dose (1p+1) may maintain similar levels of protection for the community by sustaining herd immunity, once circulation of vaccine types has been controlled.Methods and analysis: We will conduct a cluster randomized trial with four intervention arms  and three unvaccinated clusters in the 27 communes of Nha Trang, central Vietnam. A PCV catch-up vaccination campaign to all children under three years of age will be performed at the start of the trial. The primary endpoint is non-inferiority of the1p+1 schedule if compared to the WHO standard 2p+1 and 3p+0 schedules in reducing vaccine serotype carriage prevalence in infants. We will also explore impact of 0p+1 schedule. A baseline and annual pneumococcal carriage surveys of 6480 participants per survey covering infants, toddlers and their mothers will be conducted.Ethics and dissemination: Ethical approvals were obtained from the ethical review committees of Institute of Tropical Medicine, Nagasaki University (151203149-2) and the Ministry of Health, Vietnam (1915/QD-BYT). The results, interpretation and conclusions will be presented at national and international conferences, and published in peer-reviewed open access journals.Trial registration number: NCT02961231 Streptococcus pneumoniae was associated with about 14.5 million episodes of serious pneumococcal disease and more than 800,000 deaths globally in children younger than five years, with the highest burden among low and middle income countries. While PCVs have substantially reduced the burden of pneumococcal disease, their high price has delayed PCV introduction among middle income countries without financial aid, and will make it difficult for low income countries that have introduced PCVs with the help of the Gavi, the Vaccine Alliance, to sustain their programs once they transition from Gavi support.Before the widespread use of pneumococcal conjugate vaccines (PCVs). The 3p+0 schedule is used in most low-income countries introducing PCV with Gavi support and aims to provide maximum direct protection early in life where young children are most susceptible to pneumococcal disease. However, almost all high-income countries are using a booster dose schedule that in addition aims to prevent transmission and hence to induce herd protection.WHO currently recommends giving three PCVs doses – either three doses in infancy (3p+0), or two doses in infancy followed by a booster around the end of the first year of life (2p+1). Hence it has been proposed that a schedule with a single priming and a booster dose (1p+1) may maintain similar levels of protection for the community by sustaining herd immunity, once circulation of vaccine types has been controlled by the use of higher dose regimens, or by a catch-up campaign.PCV programs have been designed to provide optimal individual protection of the vaccinees, yet experience in both high income and low income countries indicates that herd immunity, which is generated by reducing carriage and hence transmission of vaccine serotypes in the community, can control vaccine type pneumococcal disease in vaccinated and unvaccinated individuals alike. The UK, who had previously spear-headed the reduction from three to two priming doses, has recently decided to move to a national 1p+1 schedule.Since, it has been shown that indeed a booster schedule with only a single priming dose induces non-inferior post-booster immunogenicity if compared to a 2p+1 schedule, providing some evidence that such reduced-dose schedule could sustain herd protection as hypothesised, within this trial we investigate the feasibility of reducing the number of infant doses in the PCV immunization schedule, to make more efficient use of herd immunity in the protection against pneumococcal disease. Rather than observing differences in direct vaccines effects between schedules, our study is designed to directly observe the population level effectiveness of alternative schedules. In order to apply the study outcome in countries using either 3p+0 or 2p+1, we will include both 3p+0 and 2p+1 schedules as control arms in the study. We will also include an investigative 0p+1 arm to test whether population effectiveness can be achieved without a priming dose.Using PCV impact on vaccine type carriage as a marker of vaccine type diseaseIn summary, the following PCV schedules are investigate in this study; (i) 0p+1 – A single dose of PCV at 12 months of age, (ii) 1p+1 – A two-dose schedule of PCV at two and 12 months of age, (iii) 2p+1 – A three-dose schedule of PCV at two, four and 12 months of age, and (iv) 3p+0 – A three-dose schedule of PCV at two, three and four months of age.The cost of PCV use can be greatly reduced by making use of existing herd immunity to protect children against vaccine-type pneumococci. We will reduce the circulation of vaccine-type pneumococci to low levels using a catch-up campaign, after which we will evaluate the ability of a simplified two-dose regimen and an alternative one-dose regimen to prevent the reestablishing of vaccine-type pneumococci.To investigate the innovative use of existing and future PCVs to protect communities, in particular in resource-limited settings at lower cost using fewer doses, we will pursue two primary, four secondary and two exploratory objectives as follows:Primary objective 1. We will evaluate non-inferiority of the 1p+1 schedule compared to a 2p+1 schedule in maintaining control of VT carriage in (a) children aged 4-11 months,i.e. after the age of a completed primary series and before age eligibility of a booster dose , and (b) children aged 14-24 months,i.e. after the age where a booster dose is given (this is the beginning of the age period when most intense transmission of pneumococci is believed to occur).Primary objective 2. We will evaluate the non-inferiority of the 1p+1 schedule compared to a 3p+0 schedule in maintaining control of VT carriage in (a) children aged 4-11 months and (b) children aged 14-24 monthsSecondary objective 1. We will evaluate non-inferiority of the 0p+1 schedule compared to a 2p+1 and a 3p+0 schedule respectively in maintaining control of VT carriage in (a) children aged 4-11 months, and (b) children aged 14-24 months.Secondary objective 2. We will evaluate non-inferiority of the 1p+1 and 0p+1 schedules compared to 2p+1 and 3p+0 schedules in maintaining control of VT carriage in children from the study areas presenting to the local hospital with clinical pneumonia as part of a long-standing enhanced pneumonia surveillance in the study area.Secondary objective 3. We will measure the effect of catch-up vaccination in the community on VT carriage four months after the second dose for children eligible for catch-up vaccination.Secondary objective 4. We will develop mathematical models to predict the impact of 1p+1 and 0p+1 schedules against vaccine type carriage and disease in Nha Trang if introduced simultaneously to all clusters following a catch up campaign, and infer the impact of such schedules in other transmission settings.Exploratory objective 1. We will measure the impact of PCV vaccination in the four vaccine schedules on pneumonia incidence and the nasopharyngeal serotype distribution and load among pneumonia patients.Exploratory objective 2. We will measure the impact of PCV, delivered according to the different regimens in this study, on admissions associated with specific respiratory viruses, including influenza and respiratory syncytial virus.The study is conducted in the 27 communes of Nha Trang, central Vietnam which is the capital of Khánh Hòa province. Nha Trang is surrounded by the sea to its East and mountains elsewhere and has about 400,000 inhabitants. Of the 27 communes, eight are classified as rural and 19 as urban. Communes are an administrative unit chosen to be of approximately similar population size and are locally organizing facilities including child-care, schooling and first-line medical care. Nagasaki University has been conducting studies in collaboration with local health authorities in this study site since 2007. PCV10 (Synflorix) has been registered in Vietnam since 2016. However, PCV is yet to be introduced into the national immunization program in Vietnam and private market uptake is minimal.We will conduct a Phase IV cluster randomized trial in the 27 communes of Nha Trang city. The four different PCV schedules  form four corresponding intervention arms completed by an informal, non-randomised control arm without PCV use . The uniAt the time of initiation of the study, PCV10 was registered in Vietnam, while this was not yet the case for PCV13. Therefore, PCV10 is used in the study.. PCV10+6A type pneumococcal prevalence was 33% in healthy infants and 30% healthy toddlers.Carriage surveys among healthy children in Nha Trang as well as in hospitalized children admitted with acute respiratory infection found similar serotype coverage for both PCV10 and PCV13; approximately 65% in healthy and 70% in children with acute respiratory illnessWe assumed that (i) the baseline prevalence of carriage of PCV10 serotypes among infants in Nha Trang is 32.5% and varies between communes from 20% to 45% and (ii) that carriage prevalence is reduced to 5% through the catch-up campaign and kept at the same level through routine vaccination under a 2p+1 or 3p+0 schedule.Nasopharyngeal samples will be collected before the start of PCV vaccination in the site and at 6, 12, 24, 36, 48 and 60 months thereafter from 60 subjects per age groups  for each of the 27 clusters; adding up to 6,480 swabs per cross-sectional study and 45,360 in total. We assume that 10% of swabs cannot be obtained or cannot be interpreted in the laboratory. We calculated the number of clusters required to test our non-inferiority hypothesis under a type I error probability of 5% and 80% power. we calculated that 5.37 clusters are required to detect an increase in VT carriage prevalence among children in the 1p+1 arm compared with the 2p+1 or 3p+0 arms of 5% or more. Hence, six clusters for each intervention arm were included.As detailed in Hayes and Moulton but haven’t been investigated as a programmatic choice for routine use yet. This trial set-up posed a unique opportunity to include an additional arm that investigates the effectiveness of a 0p+1 schedule in sustaining population protection against VT carriage.The primary goal of this study is to compare the effect of PCV in a 1p+1 schedule compared to 2p+1 and 3p+0 schedules respectively. However, by extension of the concept of sustaining herd immunity with fewer doses at infancy, a single dose schedule may suffice if the lack of a priming dose does not impair the efficacy of the dose given at 12 months of age. Single PCV doses have been used successfully in toddlers and older children as part of catch-up campaigns to accelerate control of VTsi.e. being somewhat separated from the other Nha Trang communes. Vinh Luong and Vinh Phuong communes are classified as rural communes and Vinh Hoa as an urban commune. Although we will not formally consider these communes as controls for the study as they have not been part of the randomisation, inclusion of unvaccinated communes will provide information on potential year-by-year carriage variations due to introduction of new strains from outside of Nha Trang or from vaccinated communes in Nha Trang.The three northernmost communes, Vinh Luong, Vinh Phuong, and Vinh Hoa have been assigned to the unvaccinated control arm based on the geographical background,The remaining 24 communes have been randomized into the four treatment arms. To ensure random but balanced allocation of clusters that were similarly representative of rural and urban communities and that are included in the ongoing hospital-based surveillance, we used automated rejection sampling.We defined the following set of acceptance criteria:i)In each arm at least one of the six rural communes must be selected.ii)In each arm at least three of the 16 communes included in the ongoing pediatric hospital-based surveillance for acute respiratory illnesses must be selectediii)No two adjacent clusters can be assigned to the same study arm indicates that there is at least one possible sampling permutation that fulfills criteria iii). Using the statistical software R we developed an algorithm to randomly assign arms to clusters and reject a sample if it violated any of the acceptance criteria above. The program was run until the first sample fulfilled all criteria. In total, 2,793,298 samples were rejected. The final allocation is shown inThe four color theoremA catch-up vaccination campaign was done in February 2017 before the start of PCV vaccine introduction in all but the unvaccinated three communes. Three doses of PCV10 have been offered to all children between two and six months of age with an interval of two months between the first and second, and seven months between the second and the third doses. A catch-up of two doses of PCV10 has been offered to children between seven and 18 months of age with an interval of two months between the two doses. Children between 19 and 36 months of age have been offered a single dose. This was expected to quickly control circulation of vaccine serotypes. Children with known allergy to PCV10 will be excluded from the vaccination campaign.Children receive PCV based on which cluster they reside in. The detail schedule and time of the vaccination are shown in theS. pneumoniae carriage patterns while the second carriage survey after the catchup vaccination will reveal the effect of catchup vaccination and initial vaccine introduction in the community. The subsequent annual carriage surveys will reveal theS. pneumoniae carriage pattern among clusters receiving different PCV vaccination schedules.We will conduct cross-sectional nasopharyngeal carriage surveys before the catchup vaccination campaign (baseline carriage survey), four months after the second dose of catch-up vaccination (post-catchup carriage survey), and annually during the same month that the baseline survey was conducted in. In each carriage survey, 60 children four to 11 months old, 60 children 14 to 24 months old and their mothers (120) in each of the 27 study clusters will be enrolled and screened for the presence of vaccine-serotype carriage. The census database and regularly updated EPI vaccination list of children are used to randomly select study subjects. The data manager from NU will create a random list based on a list of eligible children using Stata software version 14. Informed consent will be obtained from mothers or guardians of the child before enrolment by medical doctors or health staff at commune health centers. The baseline carriage survey will reveal the backgroundS. pneumoniae lytA gene using real-time PCR. The positive samples will be cultured, DNA extracted and then the DNA samples will be transported to MCRI for serotype determination by Microarray assay, the most sensitive of serotyping methods. All the data will be double-entered and checked before the data analysis. Data managers from NIHE and NU will manage the database, and only the data without personal information will be shared with other main investigators from the London School of Health and Tropical Medicine (LSHTM) and Murdoch Children's Research Institute (MCRI) for data analysis. In accordance with the ethical approval, the residual samples will be stored for five years after completion of the study for future confirmatory testing. Clinical trial insurance contract has been obtained to cover the AE, SAE treatment cost and compensatory payments.Nasopharyngeal samples will be collected from the study participants. The initial screening test will be conducted locally at the Pasteur Institute in Nha Trang. DNA will be extracted from the nasopharyngeal samples and screened for theThe study subjects were less than 24 month-old children, eligible for routine vaccination in the community and they were not involved in the development of research question, outcome measures, the design of the study. Fieldworkers from the commune health centers conduct the home visit, explained the study and requested informed consent from the parents or guardian of the subjects to participate in the study. The results of the study will be shared with the local health authorities and the local health authorities will disseminate the study results to the parents and guardian of the participants. The parents or guardian of the children participating in the study were asked to report any discomfort or side effect of the PCV10 vaccination and nasopharyngeal sample collection during the carriage surveys. i.e. the difference between 1p+1 and 2p+1 arm VT prevalence in infants) following the approach detailed in Hayes and Moulton for trials with fewer than 15 clusters per arm. The upper limit of the two-sided 95% confidence interval of the treatment effect not exceeding the specified non-inferiority margin of 5% will indicate non-inferiority.The comparison of carriage prevalence in the intervention (1p+1 or 0p+1) clusters and the gold standard (2p+1 or 3p+0) clusters respectively will allow age-group specific assessment of non-inferiority of the 1p+1 and 0p+1 schedules if compared with the 2p+1 or 3p+0 schedules respectively in regard to protection against vaccine type carriage. The data will be analysed single-blindedly through an intention-to-treat analysis as this yields the most conservative effect that could be observed in a real-world setting. An absolute difference in prevalence of <5% will be used as the non-inferiority margin . As the primary analysis we will use a Chi-squared test of a difference in two proportions to estimate the treatment effect , the level of protection within each arm given by 1p+0 and 1p+1 (two parameters) and the rate of waning for the protection given by the 1p+1 dosing schedule. Chain convergence will be assessed through the use of the Gelman-Rubin statistic and efficient exploration of the posterior sample space will be confirmed by calculating the effective sample size. The estimated model parameters will then be used to predict the impact of PCV in a scenario where PCV had been introduced using the 1p+1 or 0p+1 schedules in all 27 communes. We will also use this framework to infer the impact of continuation with a 1p+1 or 0p+1 schedules in other transmission settings where PCVs have been in use and where high quality allows model calibration (secondary objective 4).. Nasopharyngeal swabs will be taken from children attending to Kanh Hoa Province General Hospital (KHGH), the only public hospital in Nha Trang, with signs of clinically or radiographically confirmed pneumonia and coming from the study areas as an additional means of monitoring vaccine-type carriage in the study areas. This will enable us to evaluate this strategy of sampling for monitoring potential re-emergence of VT carriage in communities using the reduced schedule approach.To address exploratory objective 1 and 2, we will monitor the incidence of pneumonia in the study areas, as a continuation of an ongoing population-based pneumonia surveillance project that has been in place in the area since 2007The trial meets the ethical and regulatory requirements to monitor serious adverse events (SAE) in line with standards of good clinical practice. A SAE was defined as any event requiring hospitalization or resulting in death. Using the ongoing surveillance for acute respiratory illnesses at KHGH, we will monitor SAE potentially related to PCV vaccination. Any SAE such as hospitalization or death of a child within one month after receiving PCV will be investigated for its association with PCV vaccination. This process is similarly conducted for routine EPI vaccines as well. The Community Health Centre (CHC), local polyclinics and the Preventive Medicine Department of Kanh Hoa Health service in Nha Trang will support and collaborate on PCV related SAE monitoring. These health care institutions are also involved in the SAE monitoring related to EPI vaccination program in Vietnam and the safety monitoring meetings will be conducted every three-to-four months. If dangerous SAE are reported, the safety monitoring team can instruct to stop the study and report to MOH.In October 2016 the baseline carriage study was conducted, followed by PCV introduction and a catch-up campaign in accordance with randomization in January and February 2017. The year 5 post introduction survey, expected to take place in October 2021, was postponed to 2022 July due to the COVID-19 outbreak situation in Vietnam and analyses for primary endpoints are expected to be completed by first quarter of 2023.Ethical approval was obtained by Ministry of Health, Vietnam (4875/QD-BYT), and Nagasaki University (15120149).Strengths and limitations of this study. This study is designed to address whether a reduced PCV dosing schedule of one primary and one booster (1p+1) can be applied in a population with herd immunity against vaccine type PCV.This study includes a PCV catch-up vaccination followed by a cluster randomized trial with four PCV intervention arms  and three unvaccinated clusters in a PCV naïve population.The primary outcome is the non-inferiority of vaccine type pneumococcal carriage among children in 1p+1 arm cluster compared to WHO recommended 2p+1 and 3p+0 arms clusters.Limitations of the study include limited power for secondary outcomes. This article describes a hotly-anticipated trial of pneumococcal conjugate vaccine schedules taking place in Vietnam. The optimal schedule for infants, balancing control of vaccine-serotype pneumococcal disease and the high cost of pneumococcal conjugate vaccines, has been a subject of extensive debate in the pneumococcal and vaccinology communities in recent years. The design of this trial seeks to directly compare vaccine serotype carriage in populations receiving either (presumed) 0, 1, 2, or 3 doses of pneumococcal conjugate vaccines during infancy. A catch-up campaign for children 3 and under was implemented following randomization but prior to beginning the experimental vaccine schedules. The COVID-19 pandemic interrupted the expected sampling intervals following introduction of the experimental schedules.  Like many in the field, I am intensely curious to see the results of this trial, in particular, with regard to the conduct of the trial  and, of course, the results. How many doses of pneumococcal conjugate vaccine are sufficient to control the circulation of vaccine-serotype carriage in a naive population? How long does protection against vaccine serotype carriage from the booster dose last? What happens in the unvaccinated regions? What is carriage like in adults? This will be a provocative and enlightening trial, and I will look forward to seeing the results.Is the study design appropriate for the research question?YesIs the rationale for, and objectives of, the study clearly described?YesAre sufficient details of the methods provided to allow replication by others?YesAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:pneumococcal epidemiology, pneumococcal vaccine effectiveness, pneumococcal vaccine schedulesI 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 study titled "Evaluation of the effect of reduced-dose pneumococcal conjugate vaccine schedules on vaccine serotype carriage in children and their caretakers in a naïve population in Vietnam: Protocol for a cluster randomized non-inferiority trial" by Yoshida et al. (2023) holds significant importance in evaluating the efficacy of reduced-dose pneumococcal vaccination regimens. If the findings of this study confirm that the reduced-dose schedule is as effective as the WHO-recommended higher-dose schedule, it could have profound implications for the global control of pneumococcal disease, especially in the low- and middle-income countries (LMICs). Given the high cost of pneumococcal vaccines, a reduced-dose schedule could yield substantial cost savings and play a pivotal role in sustaining pneumococcal vaccinations programs even with no or reduced support from the organisation like GAVI especially in the LMICs. Furthermore, this research aims to address a crucial question: whether administering a single vaccine dose at 12 months of age, as part of the catch-up schedule, is adequate for conferring protection against pneumococcal disease in later age. While the recommendation for this one-dose catch-up schedule exists, empirical evidence to support it is currently lacking. Therefore, the outcomes of this study have the potential to significantly impact global efforts to prevent the burden of pneumococcal disease. Considering all those discussed above, I strongly recommend to public this study. This is a very well-written manuscript. However, I have some minor comments for the authors for consideration to improve the clarity. Below are my specific comments.The schedules of the vaccine, such as 3p+0, 2p+1 has not been clearly defined in the abstract. Introduction:Again, vaccination schedules have not been defined adequately. However, they have been clearly described in Figure 1, so it is good to define clearly in the introduction and refer Figure 1.This study is going to evaluate the effectiveness of a single-dose pneumococcal vaccination at 12 months of age, as part of the catch-up schedule. I think, it would be good to provide some data if available on the effectiveness of 0p+1 dose schedule. If there are no studies evaluating the effectiveness of 0p+1 schedule, I think, that would be worth mentioning in the introduction. Methods:Primary objective: It is good to define the non-inferiority, i.e. non-inferiority margin.Study endpoints- I think it is also good to provide a justification of using VT carriage as a study endpoint instead of the more specific outcome, VT invasive pneumococcal disease.Secondary objective 2: In the previous objectives, the authors clearly mentioned that the efficacy of the schedule will be measured for two different age groups, but for secondary objective 2, they have not mentioned whether they will evaluate the efficacy for different age groups or for all children. If there is no budget constraint, I would recommend to do a vaccine-type IPD surveillance to measure the effectiveness of the vaccine against the more specific outcome.Secondary objective 4: I think the analysis for objective 4 is conditional on the other previous objectives. If the reduced-dose schedules are not effective at the desired level, it is not worth having a predictive model for the reduced-dose schedule.Sample size calculations: This section has not been clearly written. For example, what was the non-inferiority margin and how the design effect has been adjusted. As this paper will be cited by other papers arising from this study, I would recommend to write the sample size calculation section in more detail.Approaches and data analysis: It seems to me that the statistical analysis section is inadequate. The study has several objectives, but the authors only have written the statistical analysis methods for the primary objectives not for the secondary ones. For example, the statistical analysis method might be different for secondary objective 2 as they will have a passive surveillance data for the study endpoints. Hazard ratio (Cox regression model) can be used to measure the effectiveness of the new schedules for this objective. Finally, I would like to thank all the authors for their effort in addressing this important and timely research question. Abstract:Is the study design appropriate for the research question?YesIs the rationale for, and objectives of, the study clearly described?YesAre sufficient details of the methods provided to allow replication by others?PartlyAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:Infectious disease, vaccine evaluation, 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. General comments: At the outset I would like to congratulate the authors for taking up this important gap to explore. There has been a constant trade-off between higher prizes of PCV and reduction in doses or schedule, especially for programmatic consideration in LMIC which carries the highest burden of IPD. This seems to be completely new strategy for PCV program for those countries who can’t afford and sustain PCV in regular program. Once the pneumococcal transmission is controlled to a very low level by catch-up vaccination, we can maintain the level of herd protection by either of 1p+1 (younger age) or 0p+-1 (elder age) PCV schedule. This could be a cost effective option. Observing the population level effectiveness of alternative schedules will be of great help in deciding the programmatic inclusion of PCV. Overall, this is a greatly written protocol where all the aspects of design and conduct of clinical trials have been considered.Specific comments:Abstract:Introduction: Sentence “three doses in infancy with Pentavalent vaccine (3p+0)” might be misinterpreted by readers considering P as abbreviation for “pentavalent”. We know that 3p+0 is “three primary doses with no booster”. Therefore, to avoid confusion, can we say, “three primary doses in infancy with Pentavalent vaccine”?Main Text:Introduction: I suggest adding 1p+1 evidence of noninferiority of schedule in VT carriage reduction from other countries South Africa, Cuba, India to make your case stronger.Hypothesis: Can you rewrite in the hypothesis format? Like: ‘We hypothesized that the reduced dose schedules of PCV; two doses and single dose schedules, are similarly effective in maintaining herd protection.”Objectives: Needs some clarity.Primary objective:Your primary objective is comparison of schedule in maintaining control of VT carriage. So, it will be prudent if you could define “maintaining control of VT carriage” . Or, what do you mean by control of VT carriage? And whether this estimation will be population based? And is this same for both the age groups? (4-11 months and above 11 months).Secondary objective 1: Are both the schedules combined or analyzed separately?Secondary objective 2: Are the schedules compared for effectiveness in preventing clinical pneumonia? Are the schedules combined or analyzed separately?Secondary objective 3: If we are taking samples four months after second dose then are we excluding 3+0 recipients?Exploratory 1: clinical outcome, will it be a part of “pneumonia surveillance or this protocol?Exploratory 2: Impact on RSV & influenza : are we considering only hospital admission or less severe infection also?For both exploratory objectives are you taking different bio-sampling  for clinical care or research purpose? Is separate consent needed?Population:Please enumerate common serotypes at baseline in infants & in under 5 children.Effect on Caretaker: Although it is mentioned in the title, objective & endpoints related to caretaker are not found. I suggest adding.Design:Cluster and Sample size calculation: This section says, “We assumed that (i) the baseline prevalence of carriage of PCV10 serotypes among infants in Nha Trang is 32.5% and varies between communes from 20% to 45% and (ii) that carriage prevalence is reduced to 5% through the catch- up campaign and kept at the same level through routine vaccination under a 2p+1 or 3p+0 schedule.” If I understood correctly, this means you expect that the pre-vaccination (catch-up) carriage prevalence will be reduced from 20-45% to 5%. This percentage reduction will be 75% for baseline carriage of 20% (20-5*100/20) and will be almost 90% [88.8%] for baseline carriage of 45% (45-5*100/45). I am not sure whether this would happen in short time span of 4 months. Request to explain.   Sample size is based on increase in VT carriage prevalence among children in the 1p+1 arm compared with the 2p+1 or 3p+0 arms of 5% or more. However, this needs to be aligned with the objective (instead of “maintaining the control”).In mathematical modelling section you have mentioned “three key groups” . Which are they?Is the study design appropriate for the research question?YesIs the rationale for, and objectives of, the study clearly described?YesAre sufficient details of the methods provided to allow replication by others?YesAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:Vaccine, infectious disease, paediatrics, public healthI 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.


Binder jetting is a highly productive additive manufacturing (AM) method for porous parts. Due to its cost-effectiveness, it is used for large components and quantities ranging from prototyping to series production. Post-processing steps like sintering or infiltration are common in several applications to achieve high density and strength. This work investigates how 3D-printed sand molds can be infiltrated with epoxy resins without vacuum assistance to produce high-strength molds for thermoforming applications. Specimens 3D-printed from different sand types are infiltrated with resins of different viscosity and analyzed for infiltration velocity and depth. The infiltration velocities corresponded well with the correlation described in Washburn’s equation: The resins’ viscosities and the saturation level were decisive. Amongst the investigated sand types commonly used in foundries, sand type GS19 was found most suitable for infiltration. However, the sand type proved to be a less relevant influencing factor than the resins’ viscosities and quantities applied. Infiltration of topology-optimized 3D-printed sand tools up to a wall thickness of 20 mm for thermoforming applications was found to be feasible. Creating reliable tooling poses significant challenges as they frequently possess intricate designs, necessitating precise dimensional accuracy, strength, excellent surface finish, and wear resistance . Often lAccording to the Wohlers Report 2022, 6.8% of organizations using AM parts are engaged in tooling applications related to polymer and sand patterns, cores, and molds, and 3.5% in metal molds or dies [Typical applications for metal tools are injection molding and die casting. Brotan et al.  suggest 3/h) and the ability to process material in granule form [Various studies have focused on utilizing additive manufacturing to fabricate tools from polymer materials. In the medical field, successful demonstrations and implementations were carried out for thermoforming plastic structures using molds made from calcium sulfate and gypsum powders and binder jetting technology ,13. Junkule form ,19.Three-dimensional-printed sand cores have already been implemented into the series production of metal castings . The binIn , the autThis observation gives the impulse to investigate the infiltration process of 3D-printed sand substrates with epoxy resins. It is intended to determine which resin and sand material systems are the most suitable for infiltration and if full infiltration is feasible to realize no-longer-massive  but rathThe infiltration of a substrate by a liquid or the penetration of a liquid in a porous substrate is preceded by a spreading and wetting phase . For preA liquid’s retraction rate is thus proportional to the radius of a capillary, the liquid’s surface tension, and the cosine of the contact angle, and inversely proportional to the liquid’s viscosity and the height of a liquid column that is already filled with liquid. Thus, the fluid’s and substrate’s properties, the wettability of the substrate material by the liquid, and the filling height of the pore columns determine the infiltration behavior .Denesuk et al.  developeWhen studying infiltration, it is important to consider the initial conditions, particularly the local fluid-powder ratios. In 3D printing, very small droplets are deposited on powder bulks. However, the infiltration kinetics fundamentally differ when comparing conventional deposition of powders to high-density powder beds that may be, e.g., realized by slurry-based 3D printing . This stVarious sand types are considered in this study to investigate the effect of the respective chemical composition, particle size, and morphology on the penetrability of binder jetted specimens. All systems are commercially available as raw material for 3D printers or print-on-demand products in already shaped condition. Three different particle size distributions of natural silica sand are investigated, as further detailed in Specimens are fabricated from these sands using binder jetting with organic binders  at standard parameters for 3D printing of sand molds and cores. Three different infiltration media are selected based on their strongly differing viscosities . For easSurface tension is determined for droplets of 6 µL (CR83-10), 5 µL (IH16), or 6 µL (LH28) using the optical contact angle goniometer and drop shape analysis system OCA 25  . A droplResin infiltration is investigated using the specimen design illustrated in All specimens are 3D printed in the upright direction, as illustrated in Three infiltration steps are performed for each infiltration experiment: Using syringes, the test specimens’ pockets are filled with 5 mL of properly mixed resin. After the infiltration medium is completely retracted, another 5 mL is added. The same procedure is repeated once the second amount of liquid is retracted. The time to complete retraction, i.e., the point at which the liquid level drops below the pocket’s flat bottom, is observed visually by the laboratory technician. It is recorded using an electronic watch with a stopwatch function with an estimated reading accuracy of 5 s. The one-factor-at-a-time (OFAT) method is chosen for experimental design. All available particle systems are tested for their infiltrability with the resin CH83-10. Moreover, the industry standard for 3D sand printing, the GS14 silica sand system, is tested with all three resin systems. All experiments are conducted with a sample size of three.For comparison between the microscopic and macroscopic behavior, infiltration is investigated on a micro-scale using the optical contact angle goniometer and drop shape analysis system OCA 25 . Here, only 15 g of each resin is mixed prior to the measurement, and droplets of 6 µL  or 8 µL (LH28) are formed and deposited on flat 3D printed substrates using the same materials as given in Analogously, with respect to the macroscopic examination setup, the infiltration velocity is determined as the average rate at which resin is drawn into a sand specimen during the first, second, and third infiltration steps .The specimens are cut in half using the precision cut-off machine Brillant 220  and photographed. Images are processed using ImageJ image processing software  to examiThe lowest infiltration velocity is observed for chromite sand. This can be attributed to the size and shape of the particles, which have a crucial effect on the flow of powders ,45. FlowPerfectly matched powder deposition and printing parameters, combined with highly flowable powders, result in homogeneous random close packing, whereas irregular packing can cause macro-voids to be preferentially located at the layer interfaces . These cThe highest infiltration velocity in this study is observed in combination with GS19 silica sand. This is noteworthy because GS19 sand has a comparable grain morphology to GS14 and GS25  and a higher grain size than GS14 but a lower grain size than GS25. The observed behavior cannot be explained by the known properties of the sand or by the equations listed above. Since the overall density of the printed parts increases with coarser grains, it is suspected that the 3D printing machine parameters  are better suited to the GS19 material system than GS14 or GS25 in terms of interlayer defects. Further investigation is needed to prove this hypothesis.Ensuring complete penetration and avoiding interfaces between infiltrated and non-infiltrated volumes is important to ensure sufficient strength and durability of sand tooling produced by binder jetting and subsequent resin infiltration. Therefore, the infiltration and propagation of the resin in the sand substrate is investigated.Thus, the vertical infiltration depth is found to correlate with the infiltration velocity. The investigations showed that the sand type influences the infiltration depth. However, within the sand types studied, the resin type is found to have a greater influence on the infiltration velocity and vertical depth. This is expected because the porosities of the printed substrates were relatively consistent while the resin properties vary widely.Among the resin properties, viscosity was found to have the greatest effect on infiltration. In this study, infiltration resins were used that did not differ significantly in surface tension and contact angle but had widely varying values of mixed viscosity . The infiltration velocities determined were in good agreement with Washburn’s equation (Equation (2)). Resin CH83-10 has a viscosity of approximately 21% of that of LH28 and were found to infiltrate at 5 times the rate of LH28. Resin IH16 exhibits a viscosity of about 47% and infiltrated at almost twice the rate. It is difficult to determine the pore radius and capillary length in the printed sand bodies that contribute to the infiltration velocity (Equation (2)). However, porosities and grain sizes of the sand specimens used in this study did not vary greatly . Thus, WRapid resin retraction is essential for an efficient and effective infiltration process in the production environment. It allows for deeper penetration within the pot life of a resin, which can be as low as 60 min, and makes it easier to apply resin efficiently without risking the formation of resin noses.Silica sand was found to be a suitable material system for resin-infiltrated tools. Epoxy resin infiltration may provide sufficient strength and durability in a thermoforming process. In this study, GS19 sand performed best in terms of infiltration. However, all sand specimens were infiltrated to a depth greater than 20 mm. GS14 or even finer sands could be used for higher surface finishes in binder jetting.Since sand specimens fully infiltrated with epoxy resin can achieve compressive strengths exceeding 100 MPa, the infiltration of topology-optimized structures using the approach proposed herein can result in highly durable thermoforming molds—a more versatile and resource-efficient manufacturing alternative compared to vacuum infusion.