Journal of Travel Medicine

BackgroundAs of 4 September 2020, a total of 53,996 monkeypox cases were confirmed globally. Currently, most monkeypox cases are concentrated in Europe and the Americas, while many countries outside these regions are also continuously observing imported cases. We aimed to estimate the potential global risk of monkeypox importation and consider hypothetical scenarios of travel restrictions by varying passenger volumes via airline travel network. MethodPassenger volume data for the airline network, and the time of first confirmed monkeypox case for a total of 1680 airports in 176 countries (and territories) were extracted from publicly available data sources. A survival analysis technique in which the hazard function was a function of effective distance was utilized to estimate the importation risk. Scenarios which selectively reduced the passenger volume from/to countries with detected monkeypox cases and increased/decreased the global passenger volume to the level of 2019 (high volume) or 2021 (low volume) regardless of monkeypox detection were considered for travel restrictions. ResultsThe arrival time ranged from 9 to 48 days since the first case was identified in the UK on 6 May 2022. The estimated risk of importation showed that regardless of the geographic region, most locations will have an intensified importation risk by 31 December 2022. Travel restrictions had a minor impact on the global airline importation risk against monkeypox. ConclusionsInstead of preventing the importation of monkeypox cases via airline networks, high risk countries should enhance local capacities for the identification of monkeypox and prepare to carry out contact tracing and isolation.

BackgroundMany countries require incoming air travellers to quarantine on arrival and/or undergo testing to limit importation of SARS-CoV-2. MethodsWe developed mathematical models of SARS-CoV-2 viral load trajectories over the course of infection to assess the effectiveness of quarantine and testing strategies. We consider the utility of pre and post-flight Polymerase Chain Reaction (PCR) and lateral flow testing (LFT) to reduce transmission risk from infected arrivals and to reduce the duration of, or replace, quarantine. We also estimate the effect of each strategy relative to domestic incidence, and limits of achievable risk reduction, for 99 countries where flight data and case numbers are estimated. ResultsWe find that LFTs immediately pre-flight are more effective than PCR tests 3 days before departure in decreasing the number of departing infectious travellers. Pre-flight LFTs and post-flight quarantines, with tests to release, may prevent the majority of transmission from infectious arrivals while reducing the required duration of quarantine; a pre-flight LFT followed by 5 days in quarantine with a test to release would reduce the expected number of secondary cases generated by an infected traveller compared to symptomatic self-isolation alone, Rs, by 85% (95% UI: 74%, 96%) for PCR and 85% (95% UI: 70%, 96%) for LFT, even assuming imperfect adherence to quarantine (28% of individuals) and self-isolation following a positive test (86%). Under the same adherence assumptions, 5 days of daily LFT testing would reduce Rs by 91% (95% UI: 75%, 98%). ConclusionsStrategies aimed at reducing the risk of imported cases should be considered with respect to: domestic incidence, transmission, and susceptibility; measures in place to support quarantining travellers; and incidence of new variants of concern in travellers origin countries. Daily testing with LFTs for 5 days is comparable to 5 days of quarantine with a test on exit or 14 days with no test.

We critically appraise the literature regarding in-flight transmission of a range of respiratory infections to provide an evidence base for public health policies for contact tracing passengers, given the limited pathogen-specific data for SARS-CoV-2 currently available. Using PubMed, Web of Science, and other databases including preprints, we systematically reviewed evidence of in-flight transmission of infectious respiratory illnesses. A meta-analysis was conducted where total numbers of persons on board a specific flight was known, to calculate a pooled Attack Rate (AR) for a range of pathogens. The quality of the evidence provided was assessed using a bias assessment tool developed for in-flight transmission investigations. We identified 103 publications detailing 165 flight investigations. Overall, 43.7% (72/165) of investigations provided evidence for in-flight transmission. H1N1 influenza A virus had the highest reported pooled attack rate per 100 persons (AR= 1.17), followed by SARS-CoV-2 (AR=0.54) and SARS-CoV (AR = 0.32), Mycobacterium tuberculosis (AR= 0.25), and measles virus (AR= 0.09). There was high heterogeneity in estimates between studies, except for TB. Of the 72 investigations that provided evidence for in-flight transmission, 27 investigations were assessed as having a high level of evidence, 23 as medium, and 22 as low. One third of the investigations that reported on proximity of cases showed transmission occurring beyond the 2x2 seating area. We suggest that for emerging pathogens, in the absence of pathogen-specific evidence, the 2x2 system should not be used for contact tracing. Instead, alternate contact tracing protocols and close contact definitions for enclosed areas, such as the same cabin on an aircraft or other forms of transport, should be considered as part of a whole of journey approach.

Global airline networks play a key role in the global importation of emerging infectious diseases. Detailed information on air traffic between international airports has been demonstrated to be useful in retrospectively validating and prospectively predicting case emergence in other countries. In this paper, we use a well-established metric known as effective distance on the global air traffic data from IATA to quantify risk of emergence for different countries as a consequence of direct importation from China, and compare it against arrival times for the first 24 countries. Using this model trained on official first reports from WHO, we estimate time of arrival (ToA) for all other countries. We then incorporate data on airline suspensions to recompute the effective distance and assess the effect of such cancellations in delaying the estimated arrival time for all other countries. Finally we use the infectious disease vulnerability indices to explain some of the estimated reporting delays.

BackgroundCountries have restricted international arrivals to delay the spread of COVID-19. These measures carry a high economic and social cost. They may have little impact on COVID-19 epidemics if there are many more cases resulting from local transmission compared to imported cases. MethodsTo inform decisions about international travel restrictions, we compared the ratio of expected COVID-19 cases from international travel (assuming no travel restrictions) to the expected COVID-19 cases arising from internal spread on an average day in May 2020 in each country. COVID-19 prevalence and incidence were estimated using a modelling framework that adjusts reported cases for under-ascertainment and asymptomatic infections. FindingsWith May 2019 travel volumes, imported cases account for <10% of total incidence in 103 (95% credible interval: 76 - 130) out of 142 countries, and <1% in 48 (95% CrI: 9 - 95). If we assume that travel would decrease compared to May 2019 even in the absence of formal restrictions, then imported cases account for <10% of total incidence in 109-123 countries and <1% in 61-88 countries (depending on the assumptions about travel reductions). InterpretationWhile countries can expect infected travellers to arrive in the absence of travel restrictions, in most countries these imported cases likely contribute little to local COVID-19 epidemics. Stringent travel restrictions may have limited impact on epidemic dynamics except in countries with low COVID-19 incidence and large numbers of arrivals from other countries. FundingWellcome Trust, UK Department for International Development, European Commission, National Institute for Health Research, Medical Research Council, Bill & Melinda Gates Foundation Research in contextO_ST_ABSEvidence before this studyC_ST_ABSCountries are at different stages of COVID-19 epidemics, so many have implemented policies to minimise the risk of importing cases via international travel. Such policies include border closures, flight suspensions, quarantine and self-isolation on international arrivals. Searching PubMed and MedRxiv using the search: ("covid" OR "coronavirus" OR "SARS-CoV-2") AND ("travel" OR "restrictions" OR "flight" OR "flights" OR "border") from 1 January - 10 July 2020 returned 118 and 84 studies respectively, of which 39 were relevant to our study. These studies either concentrated in detail on the risk of importation to specific countries or used a single epidemiological or travel dataset to estimate risk. Most of them focused on the risk of COVID-19 introduction from China or other countries with cases earlier in 2020. No study combined country-specific travel data, prevalence estimates and incidence estimates to assess the global risk of importation relative to current local transmission within countries. Added value of this studyWe combined data on airline passengers and flight frequencies with estimates of COVID-19 prevalence and incidence (adjusted for underreporting and asymptomatic cases), to estimate the risk of imported cases, relative to the level of local transmission in each country. This allows decision makers to determine where travel restriction policies make large contributions to slowing local transmission, and where they have very little overall effect. Implications of all the available evidenceIn most countries, imported cases would make a relatively small contribution to local transmission, so travel restrictions would have very little effect on epidemics. Countries where travel restrictions would have a large effect on local transmission are those with strong travel links to countries with high COVID-19 prevalence and/or countries which have successfully managed to control their local outbreaks.

Highly pathogenic avian influenza (HPAI) viruses of H5N1 clade 2.3.4.4b, are spreading worldwide, posing a threat to wildlife, domestic animals, and humans. In 2025, a multidisciplinary collaboration for HPAI H5N1 surveillance among birds within Galveston County, Texas, was initiated. Between November and December 2025, oropharyngeal and cloacal swabs were collected from wild and domestic birds reported as dead or dying by Galveston County residents. Specimens were studied with molecular assays, Sanger sequencing, virus isolation, and next-generation sequencing. Molecular evidence of HPAI H5N1 was detected in 7 of 10 (70%) birds, and the virus was successfully cultured in MDCK cells. Next-generation sequencing analysis of eight influenza A genome segments demonstrated a 4:4 gene segment reassortant constellation within clade 2.3.4.4b, consistent with genotype D1.1. Community members exposed to HPAI were offered antiviral prophylaxis. No human infections were identified. This surveillance demonstrates that community involvement combined with cross-sectoral collaboration can ensure rapid detection and characterization of circulating avian influenza viruses. Sustained local surveillance is essential for early warning, risk assessment, and prevention of virus spread to poultry, mammals, and humans.

BackgroundThe Clade Ib monkeypox virus (MPXV), newly identified in the ongoing 2024 mpox outbreak, can be more transmissible through non-sexual routes compared to the previous Clade IIb strain. With imported cases sporadically reported globally, concerns have emerged about the potential of widespread transmission in the general community after importation events. Border control measures, such as screening and quarantining of arriving travellers, may help mitigate this risk and prevent localized outbreaks in the event of global spread. MethodsWe proposed nine border control strategies and evaluated their effectiveness in reducing importation risk using 10,000 microsimulations of individual infection profiles and PCR testing results under scenarios with varying disease prevalence levels (0.01%, 0.05%, and 0.1%) in the country of origin. ResultsThe proposed border-control measures would reduce missed cases by 40.1% (39.1%-41.0%), 49.8% (48.8%-50.8%), and 58.1% (57.1%-59.0%) for predeparture, on-arrival, and both tests, respectively. Replacing the on-arrival test with a seven-day quarantine and post-quarantine testing would lower the count to 21.8% (20.9%-22.6%). Quarantine-only strategies showed a linear increase in effectiveness against duration, reaching a 90.4% (89.8%-91.0%) reduction with a 28-day quarantine. Disparities in distributions of missed case counts across strategies would become more pronounced at higher prevalence levels, with stringent approaches like quarantining followed by post-quarantine screening and 28-day quarantine keeping counts below two per 10,000 travellers, even at 0.1% prevalence. ConclusionsWhen disease prevalence in the country of origin is low (0.01%), less restrictive approaches such as single on-arrival testing or a 14-day quarantine can maintain very low imported case counts of one or below. At higher prevalences, seven-day quarantining followed by post-quarantine testing, or 28-day quarantining is required to maintain similar effects. Decision makers will face balancing importation risk management and the negative impacts of such interventions to maintain safe international travel.

On February 27th, three cases of COVID-19 were reported among Norwegians that had recently returned from Lombardy, Italy. Travellers from the region rapidly became the most common source of imported infections in the earliest stage of the Norwegian COVID-19 epidemic. The situation was exacerbated by the unfortunate temporal overlap between the Norwegian winter holidays and intense epidemic spread of COVID-19 in Northern Italy, resulting in a large number of infected travellers. Here we combined flight data on travels between Norway and Lombardy with patient-level data to determine the fraction of travellers returning to Norway that had been infected with SARS-CoV-2. Travellers returning to Norway from Lombardy contracted COVID-19 at incidence rates up to 0.02 per person-day in the period spanning February 21st and March 1st, with a clear uptick in transmission in the middle of the period. This shows an example of the infection risk in tourist destinations being several fold higher than elsewhere in the region. In Norway, this is also supported by high rates of infections among tourists returning from Austria in February and March, despite a low number of reported cases in the country at the time. The massive COVID-19 prevalence among travellers suggest that mandatory quarantine of returning travellers or suspension of non-essential international flights is essential if the aim is to control or suppress the COVID-19 pandemic.

BackgroundCOVID-19 has proven to be more difficult to manage for many reasons including its high infectivity rate. One of the potential ways to limit its spread is by controlling international travel. The objective of this systematic review is to identify, critically-appraise and summarize evidence on international travel-related control measures. MethodsThis review is based on the Cochrane review: International travel-related control measures to contain the COVID-19 pandemic and followed the same methods. In brief, we searched for clinical and modelling studies in general health and COVID-19-specific bibliographic databases. The primary outcome categories were (i) cases avoided, (ii) a shift in epidemic development and, (iii) cases detected. Secondary outcomes were other infectious disease transmission outcomes, healthcare utilisation, resource requirements and adverse effects if identified in studies assessing at least one primary outcome. ResultsWe assessed 66 full-text articles that met with our inclusion criteria. Seventeen new studies (modelling = 9, observational = 8) were identified in the updated search. Most studies were of critical to moderate risk of bias. The added studies did not change the main conclusions of the Cochrane review nor the quality of the evidence (very low to low certainty). However, it did add to the evidence base for most outcomes. ConclusionsWeak evidence supports the use of international travel-related control measures to limit the spread of COVID-19 via air travel. Real-world studies are required to support these conclusions.

IntroductionThe assessment of empirical epidemiological data is needed to assess the transmissibility of SARS-CoV-2 in aircraft settings. This review summarises reported contact- tracing data and evaluates the secondary attack rates (SAR) and factors associated with SARS- CoV-2 transmission in aircraft, to provide insight for future decision making in the context of future respiratory pandemics. MethodsThis scoping literature review assessed studies published between December 2020 to November 2023 in Ovid Medline, Embase and Cochrane Library databases. The inclusion criteria were based on the PCC framework (P-Population, C-Concept, C-Context). The study population was restricted to passengers and crew (population) to assess transmission (concept) in an aircraft setting (context). ResultsThirty-one studies which assess SARS-CoV-2 transmission in 521 domestic and international flights were included in this systematic review. The SAR reported in the studies with an identified index case ranged from 0% to 16%. Significant variation in the reporting across studies was noted. Overall, the studies reported that using face masks or respirators by passengers and crew members during flight seemed to be a possible strategy for mitigating SARS-CoV-2 transmission while sitting within close proximity to index cases ([&le;]2 seats in every direction) was associated with a higher SAR. ConclusionsOur results are consistent with sporadic clusters happening onboard aircraft. Close proximity to COVID-19 cases within the aircraft was associated with a higher SAR. Our findings further underscore the need for a systematic approach to examining and reporting SARS-CoV-2 transmission onboard aircraft. This evidence may assist policymakers and transportation authorities in the development of emergency preparedness measures and travel guidance during the post-pandemic COVID-19 era.

ObjectiveTo assess the efficacy of policies designed to reduce the risk of international travelers importing SARS-CoV-2 into a country. MethodWe developed a simulation model and compared mandatory quarantine, testing, and combined quarantine and testing. We assessed the sensitivity of policy effectiveness to the timing of testing, compliance with quarantine and isolation, and other factors. ResultsIn the base scenario, a 2-day quarantine reduced more risk than testing alone. The effectiveness of a 5-day quarantine requirement with perfect compliance was similar to a 14-day quarantine with moderate compliance. Testing 72h before arrival reduced less than 10% of in-country transmission risk across all scenarios. The addition of testing to quarantine added value for shorter quarantine lengths, when testing compliance was enforced, and when testing was performed near the end of quarantine. ConclusionsQuarantine is more effective at preventing SARS-CoV-2 transmission from arriving travelers than testing alone, but testing combined with quarantine can add value if longer quarantine requirements are infeasible. Enforcing compliance with quarantine and isolation is critical. Requiring a negative test up to 72h before arrival may have limited effectiveness.

BackgroundWest Nile Virus (WNV) is a zoonotic flavivirus of significant One Health relevance and is classified as a priority pathogen with a high-risk of causing public health emergencies of global concern. WNV is endemic to Africa; however, the availability of genomic sequences from the continent remains limited. MethodsWe review the extent of polymerase chain reaction testing and genomic sequencing of WNV conducted across Africa. Using phylogeographic methods, we map the spatiotemporal spread of the virus across the continent and globally. FindingsOur study shows that WNV has been detected in 39 African countries (including Comoros, Seychelles, and Mauritius), the Canary Islands, and Reunion Island. Publications including molecular data originate from 24 countries; however, genomic sequences are publicly available for only 16 countries. We identify regions with detected viral circulation but lacking molecular surveillance. Further, we list such regions that overlap with Key Biodiversity Areas (sites harbouring significant bird diversity) as they may host high viral circulation, and high human population density that may be susceptible to spillover. InterpretationWe recognise significant knowledge gaps on the true disease burden, molecular epidemiology, and distribution of WNV in Africa. Addressing these gaps requires an integrated One Health surveillance approach which is challenging to establish. We propose three key surveillance needs as potential starting points to improve our understanding of the virus in Africa to strengthen the global public health response to this disease. FundingRockefeller Foundation, the National Institute of Health USA, Institute of Human Virology Nigeria, Global Health EDCTP3 Joint Undertaking, the Health Emergency Preparedness and Response Umbrella Program, managed by the World Bank Group, the Medical Research Foundation, and the Wellcome Trust.

BackgroundThe rapid global spread of coronavirus disease (COVID-19) is unprecedented. The outbreak has quickly spread to more than 100 countries reporting over 100,000 confirmed cases. Australia reported its first case of COVID-19 on 25th January 2020 and has since implemented travel restrictions to stop further introduction of the virus. MethodsWe analysed daily global COVID-19 data published by the World Health Organisation to investigate the spread of the virus thus far. To assess the current risk of COVID-19 importation and local spread in Australia we predict international passenger flows into Australia during 2020. FindingsOur analysis of global data shows that Australia can expect a similar growth rate of reported cases as observed in France and the United States. We identify travel patterns of Australian citizens/residents and foreign travellers that can inform the implementation of new and the alteration of existing travel restrictions related to COVID-19. InterpretationOur findings identify the risk reduction potential of current travel bans, based on the proportion of returning travellers to Australia that are residents or visitors. The similarity of the exponential growth in the epidemic curve in Australia to other countries guides forecasts of COVID-19 growth in Australia, and opportunities for drawing lessons from other countries with more advanced outbreaks.

The global spread of infectious diseases was influenced by human movement dynamics, particularly for highly transmissible diseases like COVID-19. Asymptomatic COVID-19 cases lacked symptoms before diagnosis, posing a challenge for containment. Their contribution to air travel remains understudied. This retrospective cross-sectional study investigated the role of asymptomatic COVID-19 cases in air travel and their impact on the global spread of the virus. Through our analysis of 11,775 COVID-19 cases in Hong Kong (January 2020-April 2021), log-binomial regression models assessed the association between asymptomatic status and air travel behavior 14 days before diagnosis. The Wilcoxon rank-sum test compared median flight durations between asymptomatic and symptomatic cases. Results revealed two-thirds of cases with air travel history were asymptomatic, with asymptomatic airport or flight crew ten times more likely to travel than symptomatic counterparts (adjusted PRR=10, 95% CI: 4.00-25.00). For non-crew individuals, the adjusted PRR was 1.14 (95% CI: 1.12-1.16). Median flight duration for asymptomatic cases was 4.6 person-hours shorter than symptomatic ones (p<0.01). These findings highlight the significant contribution of asymptomatic cases to air travel and suggest under-detection during initial travel restrictions. Our study emphasizes proactive public health measures early in pandemics involving airborne infections, irrespective of symptom presentation.

BackgroundEffective COVID-19 response relies on good knowledge of infection dynamics, but owing to under-ascertainment and delays in symptom-based reporting, obtaining reliable infection data has typically required large dedicated local population studies. Although many countries implemented SARS-CoV-2 testing among travellers, interpretation of arrival testing data has typically been challenging because arrival testing data were rarely reported systematically, and pre-departure testing was often in place as well, leading to non-representative infection status among arrivals. MethodsIn French Polynesia, testing data were reported systematically with enforced pre-departure testing type and timing, making it possible to adjust for non-representative infection status among arrivals. Combining statistical models of PCR positivity with data on international travel protocols, we reconstructed estimates of prevalence at departure using only testing data from arrivals. We then applied this estimation approach to the USA and France, using data from over 220,000 tests from travellers arriving into French Polynesia between July 2020 and March 2022. FindingsWe estimated a peak infection prevalence at departure of 2.8% (2.3-3.6%) in France and 1.1% (0.81-3.1%) in the USA in late 2020/early 2021, with prevalence of 5.4% (4.8-6.1%) and 5.5% (4.6-6.6%) respectively estimated for the Omicron BA.1 waves in early 2022. We found that our infection estimates were a leading indicator of later reported case dynamics, as well as being consistent with subsequent observed changes in seroprevalence over time. InterpretationAs well as elucidating previously unmeasured infection dynamics in these countries, our analysis provides a proof-of-concept for scalable tracking of global infections during future pandemics. FundingWellcome (206250/Z/17/Z)

ObjectivesRemoval of zero-COVID restrictions in China led to a surge in COVID-19 cases. In response, countries imposed restrictions on Chinese travelers. However, border policies may not provide substantial benefits and their assessment depends on accurate prevalence data. MethodsWe analyzed quarantines and testing sufficient to prevent additional in-country transmission for February 13-19, 2023 based on World Health Organization (WHO) and self-reported infection rates to estimate prevalence. ResultsHere we have shown that self-reported prevalence data indicated more stringent border restrictions compared to WHO-published prevalence statistics. No travel restrictions were required for Singapore for infections to not be greater than in complete border closure, while a 1-day quarantine, 2-day quarantine, and a 3-day quarantine were indicated for England, Germany, and Scotland respectively. A 10-day quarantine, 11-day quarantine, and 13-day quarantine were required for Italy, Japan, and France, respectively, to prevent an increase in the number of within-country infections due to travel, while South Korea required a complete border shutdown. ConclusionsOur results demonstrated the necessity for accurate and timely reporting of pandemic statistics to prevent an increase in viral spread. Through the minimum-quarantine analysis, countries can use science to determine policy, minimize international friction, and improve the cost-efficiency of interventions.

Since 2020, the UK and Europe, have experienced annual epizootics of high pathogenicity avian influenza virus (HPAIV). The first during autumn/winter 2020/21 involved the detected with six H5Nx subtypes although H5N8 HPAIV dominated in the UK. Whilst genetic assessment of the H5N8 HPAIVs within the UK demonstrated relative homogeneity, there was a background of other genotypes circulating at a lower degree with different neuraminidase and internal genes. Following a small number of summer detections of H5N1 in wild birds over the summer of 2021, autumn/winter 2021/22 saw another European H5 HPAIV epizootic, that has dwarfed the prior epizootic. This second epizootic was dominated almost exclusively by H5N1 HPAIV, although six distinct genotypes were defined. We have used genetic analysis to evaluate the emergence of different genotypes and proposed reassortment events that have been observed. The existing data suggests that the H5N1 circulating in Europe during late 2020, continued to circulate in wild birds throughout 2021, with minimal adaptation, but has then gone on to reassort with AIVs in the wild bird population. We have undertaken an in-depth genetic assessment of H5 HPAIVs detected in the UK, over the last two winter seasons and demonstrate the utility of in-depth genetic analyses in defining the diversity of H5 HPAIVs circulating in avian species, the potential for zoonotic risk and whether incidents of lateral spread can be defined over independent incursion of infection from wild birds. Key supporting data for mitigation activities. ImportanceHigh pathogenicity avian influenza virus (HPAIV) outbreaks devastate avian species across all sectors having both economic and ecological impacts through mortalities in poultry and wild birds, respectively. These viruses can also represent a significant zoonotic risk. Since 2020, the UK has experienced two successive outbreaks of H5 HPAIV. Whilst H5N8 HPAIV was predominant during the 2020/21 outbreak, other H5 subtypes were also detected. The following year there was a shift in subtype dominance to H5N1 HPAIV, but multiple H5N1 genotypes were detected. Through thorough utilisation of whole-genome sequencing, it was possible to track and characterise the genetic evolution of these H5 HPAIVs in UK poultry and wild birds. This has enabled us to assess the risk posed by these viruses at the poultry:wild bird and the avian:human interface and to investigate potential lateral spread between infected premises, a key factor in understanding threat to the commercial sector.

BackgroundDecisions to impose temporary travel measures are less common as the global epidemiology of COVID-19 evolves. Risk-based travel measures may avoid the need for a complete travel ban, however evaluations of their effects are lacking. Here we investigated the public health effects of a temporary traffic light system introduced in the United Kingdom (UK) in 2021, imposing red-amber-green (RAG) status based on risk assessment. MethodsWe analysed data on international flight passengers arriving into Scotland, COVID-19 testing surveillance, and SARS-CoV-2 whole genome sequences to quantify effects of the traffic light system on (i) international travel frequency, (ii) travel-related SARS-CoV-2 case importations, (iii) national SARS-CoV-2 case incidence, and (iv) importation of novel SARS-CoV-2 variants. ResultsInternational flight passengers arriving into Scotland had increased by 754% during the traffic light period. Amber list countries were the most frequently visited and ranked highly for SARS-CoV-2 importations and contribution to national case incidence. Rates of international travel and associated SARS-CoV-2 cases varied significantly across age, health board, and deprivation groups. Multivariable logistic regression revealed SARS-CoV-2 cases detections were less likely among travellers than non-travellers, although increasing from green-to-amber and amber-to-red lists. When examined according to travel destination, SARS-CoV-2 importation risks did not strictly follow RAG designations, and red lists did not prevent establishment of novel SARS-CoV-2 variants. ConclusionsOur findings suggest that country-specific post-arrival screening undertaken in Scotland did not prohibit the public health impact of COVID-19 in Scotland. Travel rates likely contributed to patterns of high SARS-CoV-2 case importation and population impact.

International travel poses substantial risks for continued introduction of SARS-CoV-2. As of the 17th August 2020, travellers from 12 of the top 25 countries flying into the UK are required to self-isolate for 14 days. We estimate that 895 (CI: 834-958) infectious travellers arrive in a single week, of which 87% (779, CI: 722-837) originate from countries on the UK quarantine list. We compare alternative measures to the 14 day self-isolation (78.0% effective CI: 74.4-81.6) which could be more feasible long-term. A single RT-PCR taken upon arrival at the airport is 39.6% (CI: 35.2-43.7) effective, or equivalently, it would only detect 2 in 5 infectious passengers. Alternatively, testing four days after arrival is 64.3% (CI: 60.0-68.3) effective whereas a test at the airport plus additional test four days later is 68.9% (CI: 64.9-73.0) effective. Rapidly implementing control measures for travellers from risky countries is vital to protect public health; this methodology can be quickly updated to assess the impact of any further changes to international travel policy or disease occurrence.

BackgroundVietnam has emerged as one of the worlds leading success stories in responding to COVID-19. After prolonged zero-low transmission, a summer outbreak of unknown source at Da Nang caused the countrys first COVID-19 deaths, but was quickly suppressed. Vietnam recently reopened its borders to international travelers. Understanding the attendant risks and how to minimize them is crucial as Vietnam moves into this new phase. MethodsWe create an agent-based model of COVID-19 in Vietnam, using regional testing data and a detailed linelist of the 1,014 COVID-19 cases, including 35 deaths, identified across Vietnam. We investigate the Da Nang outbreak, and quantify the risk of another outbreak under different assumptions about behavioral/policy responses and ongoing testing. ResultsThe Da Nang outbreak, although rapidly contained once detected, nevertheless caused significant community transmission before it was detected; higher symptomatic testing could have mitigated this. If testing levels do not increase, the adoption of past policies in response to newly-detected cases may reduce the size of potential outbreaks but will not prevent them. Compared to a baseline symptomatic testing rate of 10%, we estimate half as many infections under a 20% testing rate, and a quarter as many with 40-50% testing rates, over the four months following border reopenings. ConclusionsVietnams success in controlling COVID-19 is largely attributable to its rapid response to detected outbreaks, but the speed of response could be improved even further with higher levels of symptomatic testing.