Journal of Travel Medicine

During the 2026 Bundibugyo virus disease outbreak in the Democratic Republic of the Congo and Uganda, we projected potential airline-mediated importation risk using contemporary airline network and an externally calibrated Ebola importation hazard. Effective-distance analyses identified major international hub countries, including Belgium, France, South Africa, Kenya, and the United Arab Emirates, as higher-probability gateways within 30 days. These early projections provide a reproducible framework for real-time international situational awareness, while emphasizing that importation risk does not imply local transmission risk.

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.

This paper investigates COVID-19 exported cases by country and the time it takes between entry until case confirmation for the exported cases using publicly available data. We report that the average days from entry to confirmation is 7.7, 5.0 and 4.7 days for travelers from China, Italy, and Iran respectively. Approximately, one-third of all exported cases were confirmed within 3 days of entry suggesting these travelers were mildly symptomatic or symptomatic in arrival. We also found that earlier exported cases from each country had a longer time between entry to confirmation by an average of 3 days compared to later exports. Based upon our data, reported exported cases from South Korea were far fewer in comparison to those from China, Italy and Iran. Therefore, we suggest that careful monitoring of likely symptomatic travelers and better public awareness may lead to faster confirmation as well as reduced transmission of COVID-19 pandemic.

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.

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.

We performed the plaque reduction neutralization test (PRNT50) using sera collected from the 26 recipients of BBV152/COVAXIN against hCoV-19/India/20203522 (UK-variant) and hCoV27 19/India/2020Q111 (heterologous strain). A comparable neutralization activity of the vaccinated individuals sera showed against UK-variant and the heterologous strain with similar efficiency, dispel the uncertainty of possible neutralization escape.

Whole-genome analysis of the earliest-detected High Pathogenicity Avian Influenza Virus (HPAIV) H5N1 clade 2.3.4.4b detected in Hannah Point, Antarctica (January 2024) reveals close relatedness to strains that circulated in pinnipeds and seabirds along the Atlantic coast of South America during the second half of 2023.

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.

During the COVID-19 pandemic the World Health Organization updated guidelines for travel measure implementation to recommend consideration of a regions specific epidemiological, health system, and socioeconomic context. As such, travel measure implementation decisions require region-specific data, analysis, and models to support risk assessment frameworks. From May 2020 to May 2021, the Canadian province of Newfoundland and Labrador (NL) implemented travel measures that required self-isolation and testing of individuals returning from out-of-province travel. We found that during the pandemic travel to NL decreased by 82%. Our best model was 135 times more likely to explain reported travel-related cases arriving in NL than a model where travel volume and infection data did not consider the Canadian jurisdiction of origin. To test an approach used in other studies, we formulated a model without considering the travel-related case data and found that this model performed very poorly. We conclude that importation models need to be supported with data describing the daily number of travel-related cases arriving in Canadian jurisdictions and daily travel volumes originating from each country and each Canadian province and territory. While there was some reporting of this information during the COVID-19 pandemic, these data were not consistently reported or easily accessible.

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.

Measles outbreaks have increased globally following the COVID-19 pandemic. We combine multiple data sets on global measles incidence, air travels, and vaccinations to assess the risk of travel-related importation and subsequent dissemination of measles in the United States in 2024, and identify months and states with higher measles outbreak risks.

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.

BackgroundAn outbreak of COVID-19 occurred on the Diamond Princess cruise ship in January and February 2020. We analysed information about cases to infer transmission dynamics and potential modes of transmission. MethodsWe collected the daily number of 197 symptomatic cases, and that of the 146 passenger cases in two categories, i.e. those who stayed and did not stay in the same stateroom. We retrieved the quarantine details and the ships 14-day itinerary. We searched the websites of national/local health authority along the cruise routes and local news using Google for locally confirmed cases associated with the ship. We obtained the design of air conditioning and sewage treatment of the ship from literature. We back-calculated the dates of infection from the epidemic curve and compared with the start of on-board quarantine. ResultsMajor infections started on Jan 28 and completed by Feb 6 for passengers except those who stayed in the same stateroom with infected individual(s). No other confirmed cases were identified among the disembarked people in Hong Kong except an 80 years old passenger. No confirmed cases were reported in three other stopovers between Jan 27-31 associated with disembarked passengers or visitors from the ship, however two Okinawa taxi drivers became confirmed cases in association with driving the ship passengers. Infection among passengers after Feb 6 was limited to those who stayed in the same stateroom with an infected passenger. Infections in crew members peaked on Feb 7, suggesting significant transmission among crew members after quarantine on Feb 5. ConclusionsWe infer that the ship central air conditioning system did not play a role, i.e. the long-range airborne route was absent in the outbreak. Most transmission appears to have occurred through close contact and fomites. Significance StatementTransmission by the long-range airborne route for SARS-CoV-2 in the 2020 Diamond Princess Covid-19 outbreak has been debated with significant implication for intervention. We found that the transmission by close contact and fomite explains the outbreak, and the central air-conditioning system did not play a role, demonstrating the importance of social distancing, good hygiene and maintaining good building ventilation for intervention.

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.

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.

The global mpox outbreak affected many Asian countries in 2023, following a sustained local transmission in Japan. Given the large population sizes and limited vaccine rollout in Asia, the potential risk of global mpox reemergence arising from Asia is of concern. Using a mathematical model incorporating heterogeneous sexual networks among MSM, calibrated to incidence data in Japan, we projected the patterns of international mpox spread across 42 Asian countries. Our simulations highlight countries at a high risk of mpox introductions, many of which were low- and middle-income countries (LMICs) in South-eastern Asia. Our analysis also suggests a shifting focus of importation risk from Eastern Asia to South-eastern Asia, and subsequently to Central, Southern and Western Asia, which roughly coincided with the observed spread patterns in 2023. Global cooperation and support are warranted, especially for LMICs with an elevated risk of mpox introduction, to minimise the risk of continued circulation in Asia and beyond.

BackgroundPre-travel testing programs are being implemented around the world to curb COVID-19 and its variants from incoming travelers. A common approach is a single pre-travel test, 72 hours before departure, such as in Hawaii; however this raises concerns for those who are incubating or those infected after pre-travel testing or during transit. We need a rapid method to assess the effectiveness of pre-travel testing programs, and we use Hawaii as our case study. MethodsWe invited travelers departing from Kahului main airport at the end of their visit to Maui (major tourist destination among the Hawaiian islands) and performed COVID-19 PCR testing. Eligible participants needed a negative pre-travel test and a Hawaiian stay [&le;] 14 days. We designed for anonymous testing at the end of travel so that travel plans would be unaffected, and we aimed for [&ge;] 70% study participation. ResultsAmong consecutive eligible travelers, 282 consented and 111 declined to participate, leading to a 72% (67-76%, 95% confidence interval) participation rate. Among 281 tested participants, two were positive with COVID-19, with an estimated positivity rate of 7 cases per 1,000 travelers. The top states of residence are California (58%) and Washington (21%). The mean length of stay was 7.7 {+/-} 0.2 days. Regarding pre-travel testing, 87% had non-nasopharyngeal tests and 66% had self-administered tests. ConclusionsThis positivity rate leads to an estimated 17-30 infected travelers arriving daily to Maui in November-December 2020, and an estimated 52-70 infected travelers arriving daily to Hawaii during the same period. These counts surpass the Maui District Health Offices projected ability to accommodate 10 infected visitors daily in Maui; therefore, an additional mitigation layer for travelers is recommended. This rapid field study can be replicated widely in airports to assess effectiveness of pre-travel programs and can be expanded to evaluate COVID-19 importation and its variants.

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.

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.

The 2026 Bundibugyo Ebola outbreak in eastern Democratic Republic of the Congo (DRC) has already generated international spread to Uganda, raising concerns about further regional and international dissemination. Using International Air Transport Association origin-destination passenger flows, we assessed relative exposure to Ebola virus disease importation into Europe under six outbreak expansion scenarios reflecting plausible pathways of geographical spread, including cross-border transmission and amplification in highly connected regional capitals. Relative exposure patterns remained largely unchanged under localized transmission in eastern DRC and border-spillover scenarios. Expansion into South Sudan generated a first structural increase in importation pressure to Europe through the connectivity associated with Juba, while hypothetical amplification in Kampala, Kigali, and Kinshasa substantially increased importation pressure and reshaped exposure patterns across Europe. Across all scenarios, France, Italy, and the United Kingdom remained among the most exposed countries. Mobility-informed scenario analyses support preparedness as the geography of the outbreak evolves.