Due to the integration of artificial intelligence with sensors and devices utilized by Internet of Things technology, the interest in automation systems has increased. One of the common features of both agriculture and artificial intelligence is recommendation systems that increase yield by identifying nutrient deficiencies in plants, consuming resources correctly, reducing damage to the environment and preventing economic losses. The biggest shortcomings in these studies are the scarcity of data and the lack of diversity. This experiment aimed to identify nutrient deficiencies in basil plants cultivated in a hydroponic system. Basil plants were grown by applying a complete nutrient solution as control and non-added nitrogen (N), phosphorous (P) and potassium (K). Then, photos were taken to determine N, P and K deficiencies in basil and control plants. After a new dataset was created for the basil plant, pretrained convolutional neural network (CNN) models were used for the classification problem. DenseNet201, ResNet101V2, MobileNet and VGG16 pretrained models were used to classify N, P and K deficiencies; then, accuracy values were examined. Additionally, heat maps of images that were obtained using the Grad-CAM were analyzed in the study. The highest accuracy was achieved with the VGG16 model, and it was observed in the heat map that VGG16 focuses on the symptoms. Developments in the fields of artificial intelligence and communication have enabled the new industrial revolution called Industry4.0 to improve production using systems that can communicate with each other and have the ability to detect and intervene in the environment. This development in modern industry has affected many areas  and agricultural production. As a result, autonomous or non-autonomous methods such as geographical information systems, early warning and recommendation systems, and monitoring and control systems to support production in agriculture have started to be applied under the name Agriculture 4.0 .The proper use of natural resources such as water and soil in agricultural production has been an important issue over the last 20 years, after being a subject of research in the past, with warnings about diminishing resources and environmental damage. Several attempts have been made to increase yields in production via methods such as mechanization, chemical use and fertilization. However, these implementations have caused environmental, social and economic problems over time. The amount of arable land is decreasing due to the improper use of fertilizers and chemicals, improper crop rotation and negligent use of natural resources. In addition, climate change, considered both cause and effect, has reduced the yield and quality of agricultural products ,4; to waSoilless culture, one of the production techniques in agriculture, is based on the principle of fulfilling the soil’s function in plant growth as the natural growing environment for plants. The nutrient and water needs of plants are provided via nutrient solution application. In regions where environmental conditions such as the climate, water and soil are unfavorable for agriculture, soilless cultivation techniques can be used to grow products of high yield and quality. The controlled nutrition of plants in soilless culture and the reuse of nutrient solutions in some soilless culture techniques ensure the proper use of resources . The conSome nutrients need to be fully supplied to the plant in order to grow with high yield and quality. These nutrients are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn) and boron (B). The plant, which has an absolute need for each element given above, presents various symptoms in the absence of these nutrients, giving growers and researchers an idea about the necessary nutritional supplement (fertilizer). With nitrogen deficiency (N-), older leaves have a lighter color than the other parts of the plant. With phosphorus deficiency (P-), the development of plants and fruits decreases, and brownness between the veins is observed in old leaves, while underdevelopment and a dark green color are observed in young leaves. With potassium deficiency (K-), the tips of plant leaves turn yellow and curl, and in plants with fruits, the fruits are deformed and discolored. With calcium deficiency (Ca-), young leaves turn yellow and leaf margins curl, while with magnesium deficiency (Mg-), discoloration between leaf veins is observed . Since tThe fact that plants show physical symptoms of nutritional deficiencies has encouraged artificial intelligence (AI) researchers to work on this topic. Many studies have been published in the literature to show that nutrient deficiencies in plants can be predicted, and necessary recommendations on fertilization can be made. In addition, the high performance of deep learning applications in image processing with convolutional neural networks (CNNs) has inspired many researchers to exploit CNNs for the detection of plant disorders . For theAzimi  determinSharma  detectedIn Taha’s study  which saSince we found no study on basil plants after our research, we set up an experiment based on the deficiencies of nitrogen, phosphorus, potassium, calcium and magnesium elements in basil. Within the scope of the study, a dataset was created for healthy plants and plants with nitrogen, phosphorus and potassium deficiencies, and then the transfer-learning-based CNN models capable of making predictions for these four classes were compared for their success in classification and their performance in feature detection. The phases of study  consisteA controlled environment is required for the application of nutrient deficiencies. Therefore, the experiment  was set At the end of the second week, 1 plant from each pot was transferred to a hydroponic medium (water culture), and 3 plants were grown in a perlite medium (substrate culture) and 3 plants were grown in a hydroponic medium for 4 weeks.In hydroponic culture, the solution in the container was changed once a week. The nutrient solution was continuously aerated using an aquarium pump. In substrate culture, plants were watered with 100 mL of the solution every 4 days. The nutrient solution prepared according to the recommended recipe  for vegeThe solution described in A healthy plant a has greIn the case of N- b, there In the case of P- c, symptoK- d developWhen symptoms appeared within 2 weeks after the experimental setup, photos were taken using a personal phone camera  with an automatic setting of 3024 × 4032 pixels. Photographs were taken 3 days a week between 8.00 and 11.00 a.m. for plants showing symptoms of nutrient deficiency. Photographs  of a sinFor each nutrient deficiency, 2 plants were separated for the test set and 4 plants were separated for the training set during the experiment. Additionally, this process was continued with the same groups throughout the experiment.Since symptoms of calcium and magnesium deficiencies were unavailable, photos of these deficiencies (Ca- and Mg-) were not included in the dataset. The dataset consisted of 4 classes and 1757 photographs  obtainedThe dataset was split into 2 groups, training and test, while the experiment was in progress. The number of images in the groups after the collection of the photographs is shown in Data augmentation  is a comBefore preprocessing, a total of 1125 images in the training set were duplicated to 10,000 images using the preprocessing methods mentioned above, the number of images has been seem in In order to prevent empty pixels that occur in photographs due to techniques such as shifting, zooming and shearing, the gaps were filled by taking the symmetry of the resulting image.Depending on the data used, the depth added to artificial neural networks via deep learning not only adds complexity to the network but may also provide better learning ability, precision and high performance. Thanks to the large number of layers in this model, new features can be discovered and evaluated in each layer, and different features can be interpreted. This added depth enables the network to perform complex tasks successfully. In addition, deep learning makes it easy to work with big data, greatly automates feature extraction and saves it from interventions such as manually making sense of the dataset and choosing algorithms accordingly . Convolutional neural networks are one of the most widely known and used types of deep learning. The CNN model is based on the imitation of human sight and the neural networks that form the visual cortex, which is why it has been commonly preferred in image and video processing research. The CNN model attempts to distinguish differences in multidimensional big data matrices received as input during training, then uses them in tasks such as object detection/segmentation, image classification, natural language processing, speech recognition and video processing ,25. The Pre-trained neural network models are preferred in many CNN applications against problems such as the inadequacy of the dataset in terms of both quantity and diversity and the long training time of the CNN architecture designed for complicated problems ,27. The Grad-CAM is an algorithm that creates a heat map  to visuaIn the study, the batch size was set to 64, and the input shape was set to . Before training of the model, preprocessing was applied exclusively to the images split for the training dataset, and new images were recorded. In addition, for applications with randomness, such as batch generation and dilution, the “seed” value was kept constant so that the models received the inputs similarly. “Imagenet” weights were set for DenseNet201, ResNet101V2, MobileNet and VGG16 pretrained CNN models. The epoch max value was selected as 100, but since the Early Stopping application was used in training, the training was terminated after 3 epochs depending on the changes in the “loss” value at different epoch values. Apart from the “loss” value, accuracy, precision and recall values were obtained during training. In the transition to the fully connected (FC) layer in the three models, flattening was performed with “GlobalAveragePooling”. In addition, the FC layer  containsAfter the training, which was started by setting the epoch max value to 100, the models were fine-tuned by un-freezing the last layers of the models with a small learning rate of This study was conducted with the Python programming language in the Jupyter Notebook development environment using a personal computer with an AMD Ryzen 7 4800H processor and NVIDIA GTX 1650Ti graphics card systems. Version 2.3.0 of the Tensorflow library was used in the deep learning applications and was set to allow for the use of the graphics card for computations.In order for the models to be considered successful after training, their success in the given tasks was compared with quantitative performance measures such as confusion matrix , accuracHeat maps  from theLow loss and high accuracy are expected in the performance results obtained from the models. MobileNet completed the trainings  faster tExcept for VGG16, the performance of the models on the test set  was closConfusion matrices  show thaThe heat maps from Grad-CAM show which pixels on the image the models concentrate on to make their predictions. In heat maps, the models are expected to focus on the plants in the images and the symptoms of the plants. Although the MobileNet model performed close to the VGG16 model in terms of training time and accuracy, the pixels it used for classification mostly did not cover the plant. Analysis of the pixels selected by the VGG16, ResNet, and DenseNet models showed that these models were able to successfully identify the distinguishing features for classification for most images. As shown in The loss value must be as low as possible to ensure the reliability of the estimate of nutrient deficiency. Since “categorical crossentropy”, which we selected as the loss function, calculates the loss value depending on the probability of the classes, a lower loss value shows the reliability of the predictions and the probability of the models to make errors. In the test results , DenseneWe tested the dataset that we created in this study. Although the dataset contains different growth stages of basil plants, the models we used for the test that performed well in detecting nitrogen, phosphorus and potassium deficiencies in basil plants, demonstrating 89.54% accuracy and 0.288 loss. It can be seen that the results are even better with the fine-tuning process. Fine-tuning improves the results to 93.82% accuracy and reduces the loss to 0.185. After fine-tuning, the dataset gives more successful results in shallower CNNs. Analysis of the calculated loss values, accuracy  and heatIncorrect fertilization in plant farming causes a decrease in product quality and yield and increases economic losses and pollution of the natural environment and resources. For correct fertilization, it is necessary to determine the deficient nutrients in the plant. The fact that nutrient deficiencies in plants manifest via physical symptoms allows us to use the CNN model to determine which element is deficient. Although the CNN model is successful in image processing, it is not widely used to control error-prone, real-time systems such as plantage, where misdirection can have negative consequences. A scarcity of data and lack of diversity are the main reasons for this. Therefore, we have created a new dataset of plant-oriented and leaf-oriented symptom images by setting up an experiment on nitrogen, phosphorus and potassium deficiencies in basil plants. The created dataset was tested with DenseNet201, ResNet101V2, MobileNet and VGG16 networks, and analysis was performed on the pixels that the models focused on when extracting features from images. In this study, difficulties were encountered, such as errors due to the presence of old-age symptoms in healthy plants in the dataset, the similarity of samples due to the early death of the plant with nitrogen deficiency and similarities between the symptoms of different element deficiencies due to light and shade. Despite this, the learning models proved successful in testing. Among the transfer learning models, DenseNet201 gave the best result, with 89.54% accuracy before fine-tuning, and analysis of the heat maps obtained from the Grad-CAM algorithm showed that it performed the classifications by focusing on the pixels covering the plant and symptoms in the images. The MobileNet model, which completed the training faster than the other models, showed high accuracy at a rate of 92.08% after fine-tuning, but analysis of the heat map showed that it used pixels that were not expected to be effective in classification. With the highest accuracy rate of 93.82% after fine-tuning, the VGG16 model focused on symptoms unlike the other models and achieved the highest performance for our dataset. In this study, we focused on testing a new plant to create a detailed dataset and we achieved successful results in our studies with transfer learning models. The basil plant grows within a short period of time, so it is helpful to add different growth stages to the dataset. In addition, the rapid response of the basil plant to changes in the environment speeds up the image acquisition process. These factors support the improvement and elaboration of the dataset by setting up new experiments on basil. In future studies, other nutrient deficiencies, especially Ca and Mg deficiencies, will be included in the dataset; when considering that more than one nutrient deficiency may occur at the same time, different combinations of deficiencies will be included in the dataset; symptoms of an excess of nutrients will be included in the dataset and the dataset will be diversified with these implementations. Then, a model will be trained to test in a greenhouse environment. Given the excess of some nutrients in the environment, an unsuitable pH value of the environment, etc., nutrient deficiencies, can be seen, so adding environmental and biotic causes to the system as additional data for detecting nutrient deficiency is planned. In addition, we planned to design a model that is superiorly successful in regard to nutrient deficiencies in basil and functions with the right pixels in feature extraction.


Objective The aim of the present study was to perform a comprehensive review of the literature to provide a complete and clear picture of isthmocele—a hypoechoic area within the myometrium at the site of the uterine scar of a previous cesarean section—by exploring in depth every aspect of this condition.Methods A comprehensive review of the literature was performed to identify the most relevant studies about this topic.Results Every aspect of isthmocele has been studied and described: pathophysiology, clinical symptoms, classification, and diagnosis. Its treatment, both medical and surgical, has also been reported according to the actual literature data.Conclusion Cesarean section is the most common surgical procedure performed worldwide, and one of the consequences of this technique is isthmocele. A single and systematic classification of isthmocele is needed to improve its diagnosis and management. Further studies should be performed to better understand its pathogenesis. Cesarean section (CS) is one of the most common surgical operations performed worldwide.Cesarean scar defect—also called isthmocele, niche, diverticulum or pouch—was first described by Poidevin in 1961Isthmocele can be defined as a hypoechoic area within the myometrium of the lower uterine segment, reflecting a discontinuation of the myometrium at the site of the uterine scar of a previous CS..Bij de Vaate et alisthmocele, niche, cesarean section defect, cesarean section scar, cesarean section diverticulum, and cesarean section pouch. Different combinations of the terms were used. The filters used were studies conducted in humans, systematic reviews, trials, meta-analyses, and multicentric trials. Moreover, the references in each article were searched in order to identify potentially missed studies.A review of the literature was conducted to identify the most relevant studies reported in the English language. We have searched the PubMed MEDLINE electronic database, the International Prospective Register of Systematic Reviews (PROSPERO) database, the Cochrane Database, the Centre for Reviews and Dissemination (CRD) database, the Database of Abstracts of Reviews of Effects (DARE), and the National Institute for Health Research (NHS) database and studied all the articles published until October 2017. The keywords used were: The research led to the retrieval of 105 articles; other 3 articles and 1 book were added manually. Thirty articles were excluded from our research. The exclusion criteria were: articles not in English, not relevant to the review, and abstracts. We have divided the articles following the grades of recommendations and levels of evidence proposed by the Oxford Centre for Evidence-Based Medicine, as shown in The pathophysiology of the development of isthmocele is still unclear, although many authors have studied the associated risk factors.Very low uterine incisions are reported to be independent risk factors for the development of isthmocele.Another plausible factor is the closure technique, that is, double- versus single-layer closure.Ceci et al,The hypothesis might be that not closing the deeper muscular layer leads to a disrupted myometrium and to the development of isthmocele.Another proposed hypothesis is the surgery itself.Patient factors may play a role in isthmocele and in the CS healing process, due to individual differences.We still do not know why some patients develop caesarean scar defects while others do not. Probably, a single individual genetic predisposition along with other unknown factors might be the key to this phenomenon. Further studies are needed to answer this question.As first described by Morris in 1995,Infertility may also represent a big issue for patients with CS defects. The lower fertility rate might be related to the persistence of menstrual blood in the pouch, which affects the cervical mucus, as well as sperm motility and implantation.Even though it is rare, isthmocele might lead to the formation of an abscess due to the collection of mucus and menstrual blood, which act as an infection-promoting factor.Since 1990, when first described by Chen et al,Isthmocele has been reported with several descriptions: as a triangular anechoic area, as a filling defect on the anterior isthmus, or as cystic mass between the lower uterine segment and the bladder.The residual myometrium thickness is the most useful discriminating measurement in the evaluation of isthmocele.Another important concept is the deficiency degree, introduced by Ofili-Yebovi et al,Since first described by Zilberman et al,Isthmocele may also be diagnosed by hysterosalpingography as an extension of contrast into the myometrial defect at the site of a previous cesarean hysterotomy.This imaging method, MRI, may clearly define the defect and enable a faster diagnosis when patients complain of otherwise unexplainable AUB.The treatment of isthmocele is performed to relieve symptoms. Consequently, the asymptomatic cases should not be treated.Many authors describe the effectiveness of oral contraceptives in reducing bleeding disorders correlated to isthmocele.Florio et alZhang et alTherefore, oral contraceptive pills might represent a valid option for symptomatic women who do not want to get pregnant and prefer a conservative therapy.Hysteroscopy is the gold standard procedure for uterine cavity and cervical canal exploration and is the investigation of choice for AUB.Once diagnosed, an operative hysteroscopy can be performed to treat the defect, with a technique called isthmoplasty.According to the literature, the essential parameter to perform hysteroscopy is the residual myometrial thickness; indeed, with the hysteroscopic approach, there is a risk of bladder injury and uterine perforation if the myometrium thickness at the site of the defect is < 3 mm.There is no homogeneous method to perform isthmoplasty, but almost every author uses a 9 mm resectoscope and unipolar electrical current. Gubbini et alAccording to the literature, the mean time for resectoscopic treatment varies from 8 to 25 minutes.The total amount of successful outcomes of isthmoplasty is 85.5% (59.6–100%).Good outcomes were also found regarding infertility: the majority of patients who desired to get pregnant conceived spontaneously between 12 and 24 months after the isthmoplasty.According to Zhang et al,In the last few years, the development of new technologies applied to hysteroscopy have led to new interesting therapeutic applications of minimally invasive surgery for the treatment of many pathologies.Isthmocele vaginal repair has been evaluated by many authors.With laparotomy, a complete resection of the dehiscent myometrium and an accurate uterine reconstruction can be performed.Since Jacobson et alA skilled laparoscopic surgeon can use conventional laparoscopy or robotic-assisted surgery to correct the isthmocele.The critical step of the laparoscopic procedure is to correctly identify the isthmocele.The laparoscopic approach treats symptoms by eliminating the reservoir effect of the defect, concomitantly strengthening the myometrial wall. In fact, Api et alA unified definition of CS defects should be formulated to have a unique, international terminology in order to avoid confusion in the literature. However, the main question of which surgical technique of CS diminishes the risk of scar development and its symptoms will probably remain unanswered. The clinical importance of isthmocele, however, relies on the diagnosis improvement with imaging tools. Every time we suspect the presence of isthmocele in a patient with at least one CS in her history, the first diagnostic approach should be performed with TVUS and SHG, especially in those patients with AUB, pelvic pain, infertility, and dysmenorrhea. Isthmocele treatment should be based on the history of the symptoms of the patient, on, the desire of future pregnancy, and on the characteristics of the isthmocele. Therefore, it is very important to discuss the management with the patient, although it is not possible to speculate which treatment appears to be superior to the other. It is important to highlight that treatment should be proposed only to symptomatic patients. Isthmocele is a very fertile and actual field of research due to its increased rate. Further studies are needed to prevent its development and to increase the efficacy of its management.


The effectiveness of international border control measures during the COVID-19 pandemic is not well understood. Using a narrative synthesis approach to published systematic reviews, we synthesized the evidence from both modelling and observational studies on the effects of border control measures on domestic transmission of the virus. We find that symptomatic screening measures were not particularly effective, but that diagnostic-based screening methods were more effective at identifying infected travellers. Targeted travel restrictions levied against travellers from Wuhan were likely temporarily effective but insufficient to stop the exportation of the virus to the rest of the world. Quarantine of inbound travellers was also likely effective at reducing transmission, but only with relatively long quarantine periods, and came with important economic and social effects. There is little evidence that most travel restrictions, including border closure and those implemented to stop the introduction of new variants of concern, were particularly effective. Border control measures played an important role in former elimination locations but only when coupled with strong domestic public health measures. In future outbreaks, if border control measures are to be adopted, they should be seen as part of a broader strategy that includes other non-pharmaceutical interventions.This article is part of the theme issue 'The effectiveness of non-pharmaceutical interventions on the COVID-19 pandemic: the evidence'. However, the scale and breadth of border control measures adopted during the COVID-19 pandemic are unprecedented; by early 2020, all countries had adopted some form of international border control measure, and some countries maintained the use of such measures into 2023. In addition, a more diverse set of measures was adopted during the pandemic than before, such as complete border closures, vaccination requirements for incoming travellers and centralized quarantine for inbound travellers in hotels.Prior to the emergence of COVID-19, it was assumed that the effectiveness of border control measures was low and, thus, that they are generally not worth implementing. The role of international border control measures in reducing transmission during the COVID-19 pandemic remains unclear and evaluating the effectiveness of such measures is challenging. Border control measures have been broadly defined as ‘action taken to control movement of people (travel) or trade across two or more jurisdictions with the stated intent of achieving a health goal’ [Without any intervention, we can reasonably assume that the prevalence among international travellers reflects the prevalence in the country from which a traveller originates . More pr 1.Reducing the number of infected people that cross the border in the first place, which can happen either by reducing the total number of travellers or making it less likely that infected people travel. 2.Reducing the risk of infection during international travel, which includes measures to reduce the likelihood that infected patients board a plane and transmit the infection to others. Measures such as mandatory masking or circulation of air on planes would also belong to this category; however, they are excluded from this synthesis as they overlap with environmental controls. 3.Reducing the likelihood of an imported case transmitting the virus to the susceptible local population, typically by isolating or quarantining travellers from local populations until the risk of transmission is low or zero. 4.Otherwise reducing the risk of an infected case affecting disease dynamics in the local population. For example, travel measures could theoretically stop the importation of specific variants of the virus.As of early 2023, several published systematic reviews, including three written by the authors of this paper, have examined the evidence on the effectiveness of border control measures. The first set of rapid reviews investigated the effectiveness of border control measures during the early stages of the pandemic (i.e. through June 2020) and focused largely on the effects of targeted travel restrictions imposed on travellers from Wuhan and other parts of China, as well as those from Iran, Italy and South Korea, on containment, as well as the effects of the other types of border control measures that were widely adopted in early 2020, such as symptomatic screening. Subsequent systematic reviews lengthened the time periods investigated and identified evidence on additional measures, including border closures, diagnostic-based screening and quarantine. In the absence of a synthesis of these reviews, it remains challenging to appreciate fully what has been learned regarding the effectiveness of border control measures.Theoretically, border control measures could reduce transmission into a country through at least four channels: 1.What forms of border control measures, if any, have been shown to be effective in reducing the transmission of COVID-19 during the pandemic? 2.In which locations, if any, were these measures effective? 3.At what time were such measures effective?To address this gap, we aim to synthesize the best available systematic review evidence on the effectiveness of international border control measures during the COVID-19 pandemic using a narrative synthesis approach, which is a method that enables the integration of evidence from multiple sources using a textual approach to summarize the available evidence. Specifically, our synthesis aims to answer the following research questions:. 2To answer these questions, a three-step process was followed. First, the evidence collected from existing systematic reviews of international border control measures was brought together using a narrative synthesis approach. Second, evidence from additional studies that were too recent to have been included in the published reviews is discussed. We also discuss other types of studies that provide additional insights into the effectiveness of border control measures, because the studies included in the systematic reviews may not have captured all evidence of the effectiveness of border controls. Third, we aggregate the evidence from observational studies to further understand the real-world effectiveness of border control measures during the pandemic.In aiming to identify all relevant evidence, we chose not to limit the choice of populations, interventions, comparisons and outcomes (PICO). Specifically, all systematic reviews that assessed transmission-related outcomes of any of the international border control measures described above were considered, including evidence from both modelling and observational studies conducted during the COVID-19 pandemic. —measures aimed at controlling the transmission of COVID-19 across a border; —commonly used border control measures (i.e. those adopted by many countries during the COVID-19 pandemic); —measures that are non-overlapping with other NPIs included in the Royal Society evidence review .This allowed us to focus on the following border control measures: —Border closure, which is defined as the complete restriction of both inbound and outbound travellers via a specific port  or all ports. —Travel restrictions, which are partial forms of border closure aimed only at specific jurisdictions (e.g. a flight route between two locations) or specific types of travellers (e.g. those originating/transiting in specific countries or non-citizens). There is a fine line between a partial and complete border restriction and thus at times the identified systematic reviews grouped border closures and travel restrictions together. —Screening of travellers before travel or upon arrival, which includes symptomatic screening (e.g. based on fever or other symptoms), exposure-based screening  and diagnostic testing (e.g. a PCR or rapid antigen test or antibody tests). Countries also allowed exemptions to rules for vaccinated or recently infected travellers, which are akin to screening based on immunological status, so we included them under the screening category. Usually, screening is also paired with the isolation or quarantine of people who test positive or are deemed high risk for the virus, but this varies by international context. —Quarantine, which is the physical separation of travellers not known to be infected from the rest of the public. Isolation refers to the physical separation of travellers known to be infected. However, the terms quarantine and isolation are often used interchangeably in both research and practice. Quarantine can be carried out at various locations  and can vary in duration. It can also be performed in combination with other measures, such as diagnostic testing, to assess infection status.Other forms of travel measures exist (e.g. travel advice), but there is insufficient evidence in the literature on their use during the COVID-19 pandemic and so they are not a focus of this synthesis. While not all border control measures were directed towards international borders—for example, several jurisdictions in China, Canada and Australia also imposed subnational border control measures—this review mainly focuses on the effectiveness of international border control measures. However, subnational evidence is included if it otherwise met the inclusion criteria of the systematic reviews.A key challenge in measuring the effectiveness of international border control measures is the lack of a standardized definition and typology to fully describe the universe of measures adopted during the pandemic . A detaiet al. [et al. [In the case of border control measures, five published systematic reviews have summarized evidence on their effectiveness in affecting transmission during the COVID-19 pandemic –7. Thereet al. . These s [et al. , the mosThe reviews are synthesized in the order in which they were published, allowing us to highlight the new findings in each subsequent review, note any discrepancies with previous findings, and determine if any consensus had emerged in the literature. Synthesis without meta-analysis (SWiM) guidelines were used to report the narrative synthesis . The Swiet al. [The main features of the identified systematic reviews included in this synthesis are summarized in et al.  systematStudies were also grouped according to intervention type. Since many modelling studies included border closure as the most restrictive form of travel restriction, border closure and travel restrictions were grouped together. Similarly, many studies, especially observational ones, investigated both quarantine and screening as these two measures were frequently implemented together. Subsequently, studies were grouped by whether they were modelling or observational studies. While we prioritize evidence from observational studies in our analysis, modelling studies are an important part of the evidence base, since for some interventions, especially quarantine, most of the understanding was derived from modelling studies.There was a great deal of variety in specific epidemiological outcomes investigated , both wiIn . 3 (a)n = 13) and subnational border control measures adopted within China (n = 17). One study investigated both international and subnational border control measures. All but one of these early studies were modelling studies.This early rapid review examined the effectiveness of border control measures in controlling the spread of COVID-19 during the early phase of the pandemic (studies or preprints available as of 1 June 2020). It identified 29 unique articles that investigated the effects of symptomatic screening, travel restrictions and broader forms of border control measures on epidemiological outcomes, including international (The key finding of this review was that outbound travel restrictions imposed on travellers from Wuhan (23 January 2020) and Hubei province (24 January 2020) were effective in reducing the number of cases exported to other places in China and internationally. It is estimated that 70–80% of exported cases were prevented in the weeks following the implementation of these measures. Most studies also found that earlier implementation of measures could improve effectiveness. One study estimated that by the time the Wuhan measures had been adopted, the virus had already been seeded throughout the country, and thus the Wuhan measures only had a small effect on delaying epidemics (i.e. by a few days) within China. However, the effects of the same measures were larger at the international level but became less effective over time as other Chinese cities became the major source of exported cases.Evidence on the effectiveness of additional border control measures adopted by other jurisdictions on top of the Wuhan measures is less clear. Most of the studies in this review investigated targeted border control measures against Chinese travellers (flight suspensions and/or travel bans). One modelling study found that the additional measures adopted by other countries against Chinese travellers reduced the number of exported cases only by approximately a few hundred through the end of February 2020 (relative to approx. 80 000 confirmed cases in China by the end of February 2020), partially because the Wuhan measures themselves were highly effective. Two additional studies investigated the travel ban implemented by Australia on Chinese travellers, which started on 2 February 2020. Both studies concluded that these restrictions, which were levied only against Chinese travellers from China, reduced the number of imported cases, although they differed in whether they believed it was a few hundred or a few thousand averted cases.This review also identified three modelling studies that investigated symptomatic screening and concluded that the use of such measures was unlikely to be very effective in the context of COVID-19, wherein there were few cases relative to the number of travellers and many asymptomatic cases of the disease.The only observational study included in the review investigated the effects of a comprehensive set of border control measures in Hong Kong alongside other NPIs that were all implemented between January and March 2020. The border control measures had been progressively adopted in the region, starting with the closure of border control points with mainland China in late January. This was followed by mandatory 14-day quarantine for inbound travellers, which first applied to just travellers from the mainland but eventually applied to all inbound travellers by mid-March. However, as all these measures were implemented around the same time, it was not possible to independently assess the effectiveness of border control measures in this context.Given the consistency of the findings identified in this review, it seems likely that the border control measures imposed in the early phase of the epidemic (e.g. before March) had some impact on delaying the export of cases out of China and, thus, likely delayed the establishment of outbreaks outside of China, but clearly they were insufficient to stop the pandemic. All the identified studies found that the measures imposed on Wuhan travellers by Chinese officials were likely very effective in reducing exported cases and that the additional targeted measures against Chinese travellers by other countries played some role, but both types of measures became relatively ineffective within a few weeks as other places became the dominant source of imported cases.Given the rapid review approach and the large number of modelling studies, this study opted to use a proprietary tool to assess the quality of the included studies. All but six of the studies included in this review suffered from a high or medium risk of bias because they did not adequately account for the impact of other measures in their evaluation of the effectiveness of border control measures. (b)This second rapid review also aimed to assess evidence related to travel-related controls implemented during the early phases of the COVID-19 pandemic by reviewing evidence from studies published or preprinted through 26 June 2020. It also included studies that investigated diseases other than COVID-19, but we did not focus on these findings in our synthesis. This review identified 17 modelling and eight observational COVID-19 studies. The review examined only international border control measures. It included studies that investigated full or partial border closures, entry and exit screening, and the quarantine of travellers.The review identified 12 studies  that examined the impact of international travel restrictions at the beginning of an outbreak, including studies from other international contexts such as the USA. It was found that these additional measures may have reduced the number of imported cases by 26–90% and delayed the time to an outbreak by up to 26 days. It should be noted that there is low confidence in the precision of these figures. Since many of these studies did not account for Wuhan measures, they likely overestimated the true effectiveness of the measures.The review also identified 12 studies  on screening with or without quarantine. Since this review comprised mainly studies from the early stage of the pandemic, all but two of the studies evaluated symptomatic screening strategies. The modelling studies generally assumed the effectiveness of the screening strategies in their evaluations based on assumptions on the proportion of cases that were symptomatic and could be identified by the screening methods. Nine of the studies investigated the number or proportion of infected travellers detected, while only three studies  investigated whether or not the implementation of screening made a difference to domestic transmission. Based on these last three studies, the authors of the review concluded that screening might affect outbreak dynamics, but since this was based only on a small number of studies and the overall quality of evidence was low, they believed that the evidence on screening should be interpreted with caution. In contrast to the other measures evaluated, quarantine for periods of up to two weeks was found by one modelling study to result in large and measurable decreases in the probability that a case would enter the community and thus lead to onward transmission.The review used the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool to assess the risk of bias of observational studies evaluating the real-world performance of entry and exit screening (similar to diagnostic studies), the Risk Of Bias In Non-Randomized Studies of Interventions (ROBINS-I) tool for observational studies evaluating the impact of measures, and a bespoke tool for modelling studies. At the individual study level, the authors noted several sources of meaningful bias for the studies included in the review. The review also assessed the overall certainty of the evidence using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, and observed low to very low certainty across types of border control measures and outcomes.In summary, similar to the previous review, this study found that travel restrictions were more effective than screening measures and that travel measures implemented in the early phase likely had some effect in limiting the initial spread of the virus outside China. Quarantine demonstrated promise; however, this was based on only a single identified study. (c)et al. [n = 15) observational studies than those reviews. While this review also looked at non-epidemiological outcomes, we exclude them from our narrative synthesis as these outcomes are beyond the scope of this study. Unlike previous reviews, this review grouped all forms of travel restrictions with border closures and labelled them border closure policies, making its terminology inconsistent with that of the other reviews. We did not use this method to group the underlying studies identified in this review.Building on the growing corpus of effectiveness studies published by the end of 2020, this review adopted a search strategy like that of Burns et al.  but focuDespite the larger number of studies (32 of the studies included in this review had not been reviewed in either of the earlier reviews), the overall findings of this review were consistent with the previous reviews, concluding that some forms of border control measures contributed to reducing the number of cases, slowed the progression of outbreaks and reduced spread across jurisdictions. It also found that such measures are likely to be more effective when implemented early and when coupled with measures to reduce transmission in both the exporting and the importing regions.Based on a larger number of studies that investigated the use of quarantine, it was found that the use of such measures can be highly effective in reducing transmission in countries implementing the measures. However, the studies generally used very long periods (i.e. up to 14 days), and thus the review concluded that such periods were required to achieve significant reductions in transmission. It also found that quarantines were even more effective when coupled with ‘pre-release’ testing, especially for shorter (i.e. seven-day) quarantine periods.The review also investigated the use of symptomatic screening measures and, similar to the previously described reviews, concluded that the use of such measures is unlikely to be very effective in detecting a sufficiently large proportion of infected cases; however, the underlying studies suggest that symptomatic screening methods could be improved with more sensitive screening methods, awareness of travellers, asymptomatic testing, and exit screening in the country with the initial outbreak.Using the GRADE tool for observational studies and the EVIDEM framework for modelling studies, the review found that there was a high risk of bias in about half of the observational studies due to the risk of confounding with other measures. The completeness of data also led to a high risk of bias in 73% of the observational studies. Most of the modelling studies lacked sensitivity analysis of their findings.In summary, despite the larger number of studies, the findings of this study did not substantially differ from those of the two previous reviews, but the consistent findings seem to lend more credibility to the emerging consensus that travel restrictions in the early phase of the pandemic did have some effect and that quarantine, alone or in combination with diagnostic testing, appeared to be the most effective border control measure. (d)n = 48), but in this review many of the studies were contextualized to more diverse geographical contexts that were no longer aimed at the initial containment of the virus within China.This updated review synthesized evidence from 62 studies (25 unique to this review) and was conducted by the same research group as in 2020. This time, they focused exclusively on evidence from COVID-19 but otherwise used the same methodology. Again, most studies were modelling studies , likely due to the increased use of such measures globally towards the end of 2020. Importantly, most studies also assumed that positive cases would be isolated from the public for a period (which differed across studies) to prevent onward community transmission. Symptomatic or exposure-based screening was again found to be less effective than diagnostic testing, although the studies in this review provided more support for the use of such measures than previous reviews. Diagnostic screening was again seen as a superior form of screening, and the five studies that investigated this intervention found that testing could detect 50–90% of cases, but this was very contextually specific.Twelve new studies, all modelling, investigated the effectiveness of quarantine. All found some usefulness of quarantine but differed in terms of the number of cases avoided and/or detected. Notably, the level of compliance with the measure was seen as an important determinant of effectiveness, with mandatory facility-based forms of quarantine likely to be more effective than other quarantine modalities.The combined use of testing and quarantine was evaluated separately. Notably, four observational studies found very high detection rates (68–92%) when these measures were combined, and the success varied according to the actual length of quarantine used and the frequency of testing employed.As for , this reIn summary, the review reinforced the view that some forms of travel restrictions could be effective, but that symptom-based screening was unlikely to be effective enough to warrant implementation. It also reinforced the view that quarantine of incoming travellers is likely to be among the most effective measures, especially when combined with diagnostic screening. The existence of observational data to support this conclusion is noteworthy. However, the number of studies was too small to draw firm conclusions regarding the optimal length of quarantine or testing modalities. (e)et al. [This review, which used the same search strategy as Burns et al. , describThe review found potentially high levels of effectiveness of quarantine, but the level of effectiveness varied according to the length of quarantine and levels of compliance. It was found that pre-departure microbiological (i.e. PCR-based) testing could reduce the risk of transmission during travel by 10–72%, depending on the length of time between the test and the date of travel. Finally, as in the previous reviews, the highest level of effectiveness was found when quarantine was combined with some form of diagnostic-based screening.The overall risk of bias was deemed to be critical and moderate in eight studies, and the review generally found very low certainty of evidence across all the studies investigated. In short, this review did not substantially change the emerging consensus in the literature on the effectiveness of measures but provided more evidence to support this perspective. (f)Given that this review update is currently being finalized, the following are tentative findings and are subject to modification. This update largely followed the same methodology as the previous update . A key dThis updated review identified and included 60 new studies since the previously published update, including 41 observational studies and 19 modelling studies addressing priority policy questions. Like the previous update, despite the growing evidence base, the overall findings around the effectiveness of travel measures remain largely unchanged, but this update does allow for a more nuanced exploration of some aspects of effectiveness.For example, several new studies assessed the value of repeated testing of arriving travellers at various intervals during quarantine, providing more support for the view that such strategies can shorten the required quarantine time without leading to a meaningful increase in imported infections. Specifically, four observational studies of real-world national border control measures found that countries which implemented a 14-day quarantine with multiple testing ,11 and cOther notable findings include that history of COVID-19 vaccination and/or infection, when used as a screening measure in four studies, generally performs better than other screening measures in the short term for preventing infected individuals from crossing borders. The review also identified some modelling studies assessing how variants of concern or population immunity due to COVID-19 vaccination coverage and/or previous infection influenced the effectiveness of border control measures. These studies appear to suggest, as expected, that border control measures will be less effective for more transmissible variants of concern. Some modelling studies also suggest that increasing population immunity in both the travelling and the local populations decreases the number of potentially infectious individuals, thus reducing the value of border control measures over time. (g)As of 28 February 2023, this rapid review was cited 75 times. Of the studies that cited this review, only three fit the original eligibility criteria and had been published since the most recent searches by the author team. Two of these studies represent novel additions to the evidence base, as they evaluate the effectiveness of screening measures for avoiding the importation of cases of the Omicron variant. However, from these two studies it does not appear to be possible to concretely assess whether these measures were more effective for the Omicron variant than for previous variants.. 4This narrative synthesis of the existing systematic review evidence was motivated by the desire to better understand what has been learned about the effectiveness of the various types of border control measures adopted during the COVID-19 pandemic, specifically the types of border control measures, geographical contexts and times at which these measures were most effective. Overall, the literature is consistent with several findings regarding the effectiveness of specific types of measures.First, symptomatic or exposure-based screening measures, which were among the first measures widely adopted by many countries in early 2020, were not effective enough to have had a meaningful effect on reducing importations and transmission. However, the evidence also suggests that diagnostic-based screening measures, usually in the form of pre-departure or upon-arrival PCR-based testing, increased the predictive power of screening. But at best such testing alone is unlikely to detect more than about half of potentially infected travellers. More recent studies suggest that screening based on vaccination or recent infection status was potentially even more effective than diagnostic testing in preventing importation and onward transmission.Second, the types of targeted travel restrictions levied against Chinese travellers in early 2020 likely had an immediate effect on reducing transmission, but they quickly became less effective as other jurisdictions became the major source of cases. A similar narrative emerged around targeted travel restrictions levied on travellers from Iran, South Korea and Italy, although there was less evidence based on the effectiveness of these measures. Most studies also concluded that earlier implementation generally led to higher levels of effectiveness.Third, the evidence on quarantine consistently demonstrated that it had the highest levels of effectiveness of the single interventions evaluated; however, most evidence comes from long quarantine periods (e.g. 14 days). Studies have also consistently concluded that compliance with quarantines, which tended to be lower when quarantines were self-monitored, was an important determinant of their effectiveness. Also, the literature consistently found that when coupled with diagnostic testing, quarantines were more effective and could be shortened without a substantially increased risk of transmission. A study from Korea (not included in this review) suggested that up to 95% of symptomatic cases infected with the Omicron strain of the virus would go on to develop symptoms within six days , suggestFourth, with regard to travel restrictions , much of the evidence of their effectiveness was sourced from studies of targeted measures aimed at travellers from initial hotspots  during the initial containment stage. However, countries continued to implement these measures well after widespread community transmission was established in most international contexts, and evidence of the effectiveness of these measures at those time periods is very limited. Relatedly, there is limited evidence from the included systematic review studies on the effectiveness of later rounds of border control measures aimed at stopping or slowing the importation of new variants of concern, despite the widespread use of border control measures to try to slow the introduction of new variants. In addition, the widespread adoption of international border control measures as well as domestic mobility controls globally led to an overall reduction of travel, which itself likely led to a reduction in imported cases, even in locations without border control measures in place. Similarly, border control measures adopted in one country may have effects in other countries, as travellers who would have otherwise travelled to the adopting country went elsewhere. Few studies adequately accounted for the broader effects of the pandemic and pandemic response measures in deterring or displacing international travel.Fifth, the evaluation of comprehensive border control regimes, such as those that enabled some places to maintain zero-COVID status into 2021  or 2022 (e.g. Hong Kong and mainland China), was largely excluded from existing systematic reviews because of the inclusion criteria based on the evaluation of specific border control measures. For example, in Hong Kong border control measures first began as targeted restrictions but eventually escalated into a border control regime that included mandatory quarantine for all inbound travellers, extensive pre-, upon- and post-arrival testing, and strong domestic policies to provide surveillance to detect any breakthrough cases . It is vNotably, the types of measures implemented, and thus evaluated, changed over the duration of the pandemic. This might have resulted from policymakers striving to achieve different outcomes with their border control measures over the duration of the pandemic . For example, initially the goal may have been to prevent, or at least delay, the importation of any cases, which could have prevented the establishment of COVID-19 in their jurisdictions. Once community transmission had been established, however, it might be that the goal became to reduce the number of imported cases so that they did not further contribute to domestic epidemic dynamics. Similarly, once a high level of population immunity was achieved through infection or vaccination, the value of border control measures likely decreased. Later, rounds of measures were adopted in response to the rise in the Delta and Omicron variants, as well as the re-opening of mainland China, in hopes of preventing the importation of new variants of COVID-19. In addition, some countries aimed to achieve complete local elimination (i.e. ‘zero-COVID’) whereas others clearly did not. These varied goals mean that applying a single definition of effectiveness can be problematic. While some modelling studies explored these aspects of effectiveness, the literature, and thus the associated reviews, does not provide great insights into some of these important contextual questions.While the studies included in these reviews were conducted in a diverse set of countries, there is still very limited evidence from many parts of the world. We note that there were many studies from places such as Australia, Hong Kong, Singapore and Japan, where more robust measures had been put into place and where better data to evaluate these measures existed; however, there were fewer studies from other areas . The inclusion of more or higher-quality studies from countries with more robust measures might bias the overall findings towards higher levels of effectiveness.The examined systematic reviews point to several inherent challenges in the evaluation of border control measures. Border control measures were rarely the only control measures adopted by countries during the pandemic, and few studies adequately controlled for these other interventions, likely leading to bias in their estimates of effectiveness. Only a few studies leveraged quasi-experimental study designs, which, in principle, should better control for both observed and unobserved confounders. Specific designs included, for example, the controlled interrupted time-series design , the synIn addition, the large number of modelling, versus observational, studies is another important limitation of the existing literature. Modelling studies represent abstractions of the real world, and the extent to which they reflect reality is unclear. The quality of modelling studies depends on the underlying models and assumptions used, and it is difficult to evaluate the quality of such studies in practice. On the other hand, observational studies draw on real-world data but often use study design and statistical methods that make interpretation and use of their findings challenging. Many observational studies, for example, employed ecological methods to conduct comparisons across several countries, many of which likely have very different underlying systems for tracking COVID-19 and/or very different systems for designing, implementing and enforcing border control measures. Additionally, these and other studies often involved the use of composite measures for border controls, such as the Oxford COVID-19 Government Response Tracker, rather than specific real-world border control measures; such composite measures run the risk of lumping together and comparing different types of border control measures. Many observational studies have evaluated screening and quarantine measures in a way that did not reflect large national-level policies. Only a few studies evaluated real-world border control programmes involving hundreds of thousands of travellers over extended periods of time, such as the notable studies conducted in Qatar  and the The use of the systematic review methodology also meant that many studies did not meet the eligibility criteria of the examined reviews but nevertheless can provide important insights into the effectiveness of border control measures. For example, studies of quarantine failure, which is not an intervention per se, in Australia, New Zealand and Hong Kong provide interesting insights into the operational challenges of maintaining these strict border control regimes for international travellers ,24.Also, while all observational primary studies included in the reviews drew from data on observed COVID-19 cases, phylogenetic data on the introduction of specific viral lineages in relation to the timing of border control measures can also be insightful. For example, one study found that more genetically distinct lineages in the UK had been imported from countries without a mandatory 14-day quarantine period than from countries not subject to these measures after they were introduced in the summer of 2020 . AnotherBorder control measures can be among the most economically costly of the COVID-19 control measures adopted during the pandemic. For example, evidence suggests that cross-border and informal trade account for 40% of the gross domestic product and 55.7% of employment in sub-Saharan Africa . Given tWhen the WHO declared the COVID-19 outbreak a PHEIC , which it did with the authority granted to it under the International Health Regulations , it did