Journal of Travel Medicine

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.

BackgroundIn World War 1 (WW1) outbreaks of measles were associated with high case fatality rates amongst soldiers. Recent studies have shown that survivors of acute measles can also develop immune amnesia, increasing their susceptibility to other infections. However, the impact of prior measles infection on infectious diseases during WWI remains unclear. MethodsHere, we create a searchable database documenting the medical history of 1,569 individuals from the Australian, New Zealand, and Canadian forces during WW1. ResultsWe use this novel database to show that a recent measles hospitalisation was associated with a higher chance of death for infectious diseases (excluding pandemic influenza like illness), consistent with immune amnesia. Surprisingly, a prior measles infection was associated with a significant reduction in hospitalisations duration from pandemic influenza like illness. ConclusionThese findings highlight the unique interaction between measles and pandemic influenza, contrasting with other infectious diseases, and underscore the significant health burden measles placed on young adults during WW1.

World Health Organization recommendations to reduce road deaths were examined to assess the potential reductions that could be realized in countries that have not adopted them. Data from 72 countries on recommended speeding laws, alcohol laws, and vehicle safety standards were analyzed, controlling statistically for differences in average temperatures and population density per square kilometer. Using regression coefficients, estimates of the reductions that would be realized if each countermeasure were adopted in countries not currently employing it were calculated. The coefficient on alcohol laws was not significant, but deaths in these countries would likely decline by about 23 percent if speeding laws were improved. The road death would have been about 55 percent lower if vehicle safety standards for imported vehicles had been adopted. New and used vehicles that did not adhere to the standards were sold in low-income countries. Better data identifying clusters of specific collision types (pedestrians in the dark, animals, fixed objects) could lead to the adoption of countermeasures known to be effective.

In 2014, Chikungunya virus (CHIKV) infections were reported in Kilifi, Kenya, followed by a major outbreak in Mandera County in 2016. Since then, information regarding subsequent outbreaks in Kenya has been scarce. A study on the burden and etiologies of acute febrile illnesses (AFI) in Kenya reported an increase in CHIKV cases in Mombasa between December 2017 and December 2019. In January and February 2020, another outbreak of CHIKV occurred in Dadaab-Hagadera. These recurrent outbreaks necessitated the establishment of the molecular characteristics and phylogenetic differences of the CHIKVs collected from Mombasa and Dadaab-Hagadera. The challenge of distinguishing chikungunya fever (CHIKF) from other AFIs also underscored the importance of describing predictors of laboratory-confirmed CHIKV cases versus other AFIs. Sequences generated revealed that the Indian Ocean Lineage (IOL) was associated with sporadic CHIKV outbreaks in Kenya from 2017 to 2020. When sequences were compared to the 2014 Kilifi outbreak, key mutations associated with increased CHIKV viral fitness in mosquito vectors, including E1-K211E and E2-V264A, were observed in both Dadaab-Hagadera and Mombasa samples. Time-informed Bayesian phylogenetic analysis demonstrated clear geographic structuring, with Mombasa sequences forming tightly clustered clades and Dadaab-Hagadera sequences grouping separately, indicating sustained local transmission at both sites. However, some conserved amino acid substitutions were shared between the two locations, including nsP1-A104V and E2-I94V, suggesting circulation of closely related lineages. When the association of symptoms to positive CHIKV cases was compared to other AFI symptoms, sore muscles, headache, and convulsions were significantly more common in CHIKV cases. In contrast, diarrhea was considerably less frequent in CHIKV patients. Cough, skin rash, conjunctivitis, and vomiting were not significantly associated with CHIKV infection. In regions with limited access to point-of-care diagnostics, identifying clinical symptoms that are likely to be strongly associated with CHIKV infection can be important in the differential diagnosis from other AFIs, facilitating reliable patient screening and improving diagnostic accuracy, particularly during outbreaks when timely identification of CHIKV is critical. Continuous molecular surveillance of circulating CHIKV genotypes is important as the mutations identified in these CHIKV strains continuously accumulate and may have a significant impact on control strategies.

Background. Climate change is intensifying extreme weather events (EWEs) with potentially profound consequences for zoonotic disease dynamics, yet the mechanisms linking EWEs to highly pathogenic avian influenza (HPAI) H5N1 outbreaks remain poorly characterized. The ongoing H5N1 panzootic, responsible for infection in over 500 avian and mammalian species, as well as nearly 1000 human cases and 477 deaths worldwide, provides a critical opportunity to evaluate how climate conditions shape spillover risk at landscape scales. Methods. We compiled a county-month dataset of confirmed H5N1 detections across the contiguous United States from 2022 to 2024 and integrated it with satellite-derived climate metrics, storm event data, and wild bird activity data. We trained and validated a gradient boosting machine classifier to predict outbreak risk and characterize predictor relationships. Results. Our model achieved strong discriminative performance (AUC-ROC = 0.856; AUC-PR = 0.237, representing a 7-fold improvement over chance) and high recall (0.726), supporting its utility as an early warning tool. Human population and temperature-related variables were the most influential predictors: cold temperature shocks and prolonged low temperatures were consistently associated with elevated outbreak risk, likely through enhanced environmental viral persistence, wild bird habitat compression, and allostatic stress-driven immunosuppression in reservoir hosts. Among storm variables, high wind coverage elevated risk, potentially via aerosol dispersal of contaminated particulates, while tornado activity showed an inverse relationship, consistent with documented avoidant behavior in migratory birds. Wild bird reservoir density showed a strong positive monotonic relationship with outbreak risk. Conclusions. Our analyses demonstrate that routinely available environmental and infection data can be used to predict HPAI outbreak risk at fine spatiotemporal scales. These findings demonstrate the divergent roles of short- versus long-term environmental exposures in HPAI spillover dynamics, as well as the potential for machine learning-based surveillance tools to inform targeted biosecurity interventions and early warning systems.

BackgroundSeasonal human influenza viruses can escape from antibody-mediated neutralization when amino acid changes occur in the hemagglutinin protein. Routine surveillance identified circulation of an A(H3N2) virus variant in the Netherlands with amino acid substitutions at hemagglutinin positions 158 and 189. These amino acid positions were previously responsible for antigenic change of influenza A(H3N2) viruses and potentially lead to escape of this variant from vaccine-mediated immunity. AimTo characterize the emergence and antigenic properties of N158K and K189R double substitution virus variants. MethodsWe analyzed the geographical and temporal dynamics of the double-substitution variant using a phylogeographic approach and used hemagglutination inhibition assays and antigenic cartography methods to map its antigenic properties. ResultsA(H3N2) viruses carrying K189R were first detected in Guatemala in June 2024, before subsequently gaining the N158K substitution, which was intially detected in Colombia in November 2024, followed by detection in the Netherlands in December 2024. However, detections within Europe remained almost entirely confined to the Netherlands. The proportion of viruses carrying the N158K and K189R substitutions increased to 16% - 24% per collection week of sequenced Dutch viruses during the peak of the epidemic of the 2024-2025 respiratory season. Antigenic characterization of viruses with N158K and K189R substitutions indicated that these are antigenically distinct from the A(H3N2) components of 2025-2026 Northern Hemisphere vaccines, showing 8-192-fold reduction in hemagglutination inhibition titers with antisera against the vaccine strain compared to antisera against the homologous virus. ConclusionsInfluenza A(H3N2) viruses with N158K and K189R escaped recognition by antibodies raised against the 2024-2025 and 2025/2026 Northern Hemipshere vaccine strains in hemagglutination inhibition assays. These variants circulated widely in the Netherlands during the 2024-2025 influenza season, raising concerns about reduced vaccine-mediated protection if such variants would spread more broadly during 2025-2026 Northern Hemipshere season.

In 2024, mpox cases surged in the Democratic Republic of the Congo (DRC) with cross-border spread to Burundi. We developed a transmission-dynamic model calibrated against surveillance data to understand drivers in enzootic (Clade Ia) and non-enzootic (Clade Ib) areas, and the potential impact of vaccination. In non-enzootic areas we estimated that 58-84% of transmission occurred within sexual networks. MVA-BN vaccination of sex workers could have averted 91% (95% CrI 81%-98%) of infections in Sud Kivu (DRC) but only 35% (95% CrI 26%-47%) in Bujumbura (Burundi), due to later outbreak detection. In historically enzootic Equateur (DRC), ongoing zoonotic spillover best explained sustained incidence. There, pledged Lc18m8 vaccines could have averted 42% (95% CrI 40%-46%) of infections; prioritising children improved impact. Across all settings, doubling vaccine coverage by using a single dose of MVA-BN outperformed two-dose strategies. Timely detection and tailored vaccination strategies are critical to reducing mpox burden.

BackgroundChikungunya virus (CHIKV) is an Aedes transmitted arbovirus. Demographic changes coupled with the expanding footprint of the mosquito from climate change have the potential to shift the global burden from the virus. MethodsHere we use projections of human demography and Aedes mosquitoes distribution to estimate baseline and future burden from CHIKV under different climate change scenarios in 178 countries. We then estimate the potential of vaccines to mitigate the growing burden. FindingsWe found that under RCP2.6 (an optimistic climate change scenario), the global population at risk from CHIKV will increase by 30.2% to 5.4 billion individuals. We estimated a 35% increase in annual infections, 49% increase in cases and a 128% increase in deaths. A similar impact was found under the more pessimistic RCP8.5 climate change scenario. In Europe and the Americas, the growing presence of Aedes will drive the growing case burden, with increases in human population size being key elsewhere. Ageing populations will result in major increases in the number of CHIKV-related deaths in all continents outside Africa. Vaccinating 50% of individuals aged 12y+ with a vaccine providing 70% protection against disease and 40% protection against infection would avert 29% of cases and 31% of deaths. InterpretationThese findings highlight how climate change will expand the footprint of CHIKV circulation, while demographic changes will lead to substantially increased case burden in affected countries. Vaccines will be critical to minimising this changing global burden. FundingCEPI

Despite Antarcticas geographic isolation, the first incursion of high pathogenicity avian influenza (HPAI) H5N1 was detected in the 2023/24 austral summer. Surveillance for HPAI H5N1 in Antarctica remains patchy due to logistical, financial, and infrastructure challenges, with many suspected cases remaining unconfirmed, and few viral genomes sequences available to date. Through the 2024/25 austral summer we undertook five sampling expeditions to the South Shetland Islands and Antarctic Peninsula facilitated by cruise ships/operators. Across more than 500 faecal environmental samples collected from apparently healthy penguins and marine mammals, we found no detectable evidence of HPAI H5N1. However, HPAI H5N1 was detected in all but one of the skua carcasses sampled, which, in most cases, were found within meters of penguin sub-colonies. All HPAI H5N1 viral genomes sequences from skuas on the Antarctic Peninsula fell within a single lineage, which included those genomes from skuas sampled in the 2024/25 season from the South Shetland Islands. Genomes were in a different clade to those from the Antarctic Peninsula collected in the 2023/24 austral summer. Our results confirm although the prevalence may be low, HPAI H5N1 is established in Antarctica, emphasizing the need for ongoing surveillance to monitor and mitigate threats to wildlife, even in the planets most isolated regions.

BackgroundChikungunya virus (CHIKV) infection can cause significant and long-term morbidity. CHIKV typically appears in explosive outbreaks then vanishes for decades, but evidence from longitudinal studies suggests that it may persist in some populations through low levels of subclinical infection. These epidemiologic dynamics complicate prediction of CHIKV outbreaks and intervention trial planning. Songkhla province in southern Thailand is a promising location for vaccine trials due to its recent history of CHIKV outbreaks (2008 and 2018) and emerging data suggesting low levels of interepidemic transmission. Methodology and Principal FindingsHere, we describe baseline findings from a longitudinal cohort study (2022-2024, n = 5000) of CHIKV transmission in Songkhla. We used serocatalytic models to estimate CHIKV force of infection (FOI), adjusting for risk factors including developed land use surrounding the household, access to garbage collection and clean water, and others. Baseline CHIKV seropositivity in the cohort was 34.6%. Our crude catalytic model estimated 0.0160 (95% CI: 0.0153-0.0168) annual FOI. In adjusted FOI models, a higher proportion of developed land use was associated with an increase in risk of CHIK seropositivity among participants under age 12 (OR: 1.36; 1.25-1.48), who would have been exposed only to the 2018 outbreak, but associated with a decrease in risk (OR: 0.96; 0.94-0.99) among those ages 12 and up, who would have been exposed to two or more outbreaks. ConclusionsThese findings suggest that CHIKV infection risk is highly spatially variable, with prediction complicated by historical differences in virus strain and vector. Distinct ecological patterns of exposure are consistent with the 2018-20 outbreak affecting largely urban areas, with little to no exposures in rural areas, while the 2008-09 outbreak was concentrated more heavily in rural areas. Understanding the ecological drivers of this variation has important implications for identifying regions of highest risk for a future CHIKV outbreak.

BackgroundThe emergence of the highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b in North America, beginning in February 2022, has highlighted the dynamic, unpredictable, and regionally variable risk of infections. Studies are needed to assess the spatiotemporal clustering of HPAI H5 at the interface between wild waterfowl and commercial poultry to better understand and mitigate this risk. MethodsPublicly available data on HPAI H5 detections in wild birds and commercial poultry from January 2022 to January 2026 were analyzed at the county level. Retrospective space-time permutation models were used to identify and scan for clusters with higher than expected detection rates. ResultsA total of 17,091 HPAI H5 detections were reported in wild birds across 1,467 county-level locations. Four species, Mallard (Anas platyrhynchos) (2,848 detections, 16.66%), Canada goose (Branta canadensis) (1,496, 8.75%), Green-winged teal (Anas carolinensis) (1,364, 7.98%), and Snow goose (Anser caerulescens) (1,084, 6.34%), accounted for 39.73% of detections. In commercial poultry, 532 outbreaks in turkey operations, 148 outbreaks in table-egg layer operations, 99 outbreaks in broiler chicken operations, and 89 outbreaks in commercial duck operations were reported, respectively. Several spillover events followed an east-to-west expansion. In early 2022, mallard detections preceded outbreaks in Northeast egg-layer and duck farms, while snow goose detections in the Upper Midwest coincided with turkey farm outbreaks. In the Pacific and Mountain West during summer 2022, detections in Canada geese overlapped with turkey farm outbreaks. A resurgence occurred in the Midwest (2025), with snow and Canada goose detections overlapping severe outbreaks in turkey and layer flocks. Additionally, in the Upper Midwest, Canada goose and mallard detections overlapped with outbreaks in commercial duck farms during fall-winter 2025. ConclusionsThe study findings demonstrate distinct vector-based transmission dynamics of HPAI H5 at the wild waterfowl-poultry interface. Farm biosecurity strategies must adapt to these recurrent, vector-specific risks.

ObjectiveTo estimate dengue virus (DENV) seroprevalence and assess parental vaccine perceptions among children in the US Virgin Islands (USVI). MethodsA cross-sectional serosurvey was conducted during April-May 2022 among 372 children aged 8-16 years from 15 schools across USVI. Past DENV infection was determined using a dengue IgG rapid diagnostic test. Data on demographics, dengue knowledge, and vaccine acceptance were collected from parents. Catalytic models estimated annual DENV force of infection (FOI) using seroprevalence and case data from 2010-2022. ResultsSeroprevalence among children aged 8-13 years was 47% (95% CI: 29%, 68%). FOI peaked during 2012-2013 outbreaks and remained low in other years. Only 17% of parents were aware of an approved dengue vaccine, and 25% reported they would vaccinate their child. ConclusionsNearly half of children had prior DENV infection. Despite this risk, parental awareness of dengue vaccination was low, underscoring gaps in detection, diagnosis, and preparedness for vaccine implementation. Policy ImplicationsThese data highlight the need for enhanced surveillance, public education, and targeted planning for dengue vaccine introduction in endemic US jurisdictions.

This novel study detected persistent low level infections of Elephant Endotheliotropic Herpesviruses (EEHV), that can cause highly pathogenic Elephant Hemorrhagic Disease (EHD) in Loxodonta and Elephas, and co-infection of presumed less pathogenic Elephant Gammaherpesviruses (EGHV), in skin nodule biopsies, saliva and tissues collected from 43 wild L. africana (savannah elephant) in Botswana, Kenya, South Africa and Zimbabwe; in saliva from 25 wild L. cyclotis (forest elephant) in Gabon; and in saliva collected over seven years from 7 wild-born L.africana at Six Flags Safari Park, USA; and in saliva, blood and tissues from an additional 200 L. africana in USA zoos. DNA from these samples was extracted in our USA laboratories and amplified by conventional polymerase chain reaction using three-round nested primer sets designed specifically to screen for known EEHV and EGHV genes loci and to discover new species and subtypes. Sanger sequencing of purified DNA from nearly all samples yielded unambiguous positive genetic matches to previously known Loxodonta-associated EEHV2, EEHV3A, EEHV3B, EEHV6, EEHV7A, and EGHV1B, EGHV2, EGHV3B, EGHV4B, EGHV5B and discovered novel types EEHV3C-H and EEHV7B and the prototype EGHV1B. Many of the primer sets used could also have detected known Elephas-associated EEHV1A, EEHV1B, EEHV4, and EEHV5 if present in these samples, but they did not. Our extensive library of EEHV and EGHV sequences from wild and zoo Loxodonta, (as well as from 100 zoo Elephas maximus not discussed in this review), is a significant contribution to the elephant virology community, particularly for comparing subtypes types of EEHV found in pathogenic cases of EHD in zoos as well as determining and comparing species and subtypes of EEHV present in existing zoo herds, and in individual elephants being transported between zoos, and for importation of wild elephants into existing zoo herds.

Influenza A(H3N2) subclade K virus was detected in Canada early in the 2025/26 influenza season, bearing an antigenic transition in the hemagglutinin (HA) glycoprotein. Analysis of 396 HA sequences from Canada showed antigenic divergence from 2025/26 influenza vaccine strains, consistent with partial mismatch. Phylodynamic analysis revealed sustained pre-vaccine transmission without clear post-vaccine expansion. Phylogenetic and phylogeographic analyses indicated interprovincial mixing within a highly connected metapopulation, highlighting the value of genomic surveillance for real-time epidemiologic inference and public health decision-making.

The seasonal circulation of respiratory syncytial virus (RSV) in countries such as Japan, together with the transient nature of passive immunity conferred to infants via maternal vaccination or monoclonal antibody administration, may warrant a differential strategy for those born during the RSV inter-seasonal period. Maximal effectiveness may be achieved by deferring immunisation of this cohort from birth until entry into their first RSV season using catch-up administration of monoclonal antibody through a seasonal and catch-up programme, compared with year-round administration. To estimate the benefit of seasonal and catch-up programmes in reducing RSV infant hospitalisations in Japan, we developed a static cohort model following infants through their first year of life, parameterised by Japanese data on weekly and municipality-specific RSV incidence during 2018 to 2025 and on RSV case hospitalisation risk from a health claims database study. We used Bayesian inference to estimate the effectiveness and its waning for maternal vaccine (RSVpreF) and long-acting monoclonal antibody (nirsevimab) from trial data. We estimate that year-round programme of RSVpreF or nirsevimab could reduce RSV hospitalisations from the status quo, under which only high-risk infants are eligible for monoclonal antibodies, by 46% (95% uncertainty range (UR): 31%, 65%) or 58% (95%UR: 39%, 79%) respectively. Seasonal and catch-up programmes could achieve percentage reductions of 1.1-fold (95%UR: 0.82, 1.6) or 0.98-fold (95%UR: 0.83, 1.2) compared with the year-round programme. If seasonality matches the seasonal immunisation timing, using 2024 as an example, the percentage reduction was 1.2-fold (95%UR: 0.95, 1.6) or 1.1-fold (95%UR: 0.97, 1.2), respectively, compared with the year-round programme. If protection from nirsevimab remained substantial after six months, the year-round programme would likely to be more effective. RSVpreF and nirsevimab may substantially reduce RSV infant hospitalisations in Japan. The benefit of the seasonal programmes depends on predictability of RSV seasonality and potential logistical challenges.

Influenza viruses present a significant public health risk, causing substantial illness and death in humans each year. Seasonal flu vaccines must be updated regularly, and their effectiveness often decreases due to mismatches with circulating strains. Furthermore, inactivated vaccines do not provide protection against shifted influenza viruses that have the potential to cause a pandemic. The highly pathogenic avian influenza H5N1 clade 2.3.4.4b is prevalent among wild birds worldwide and is causing a multi-state outbreak affecting poultry and dairy cows in the United States (US) since March 2024. In this study, we have generated a NS1 deficient mutant of a low pathogenic version of the cattle-origin human influenza A/Texas/37/2024 H5N1, namely LPhTXdNS1, and validated its safety, immunogenicity, and protection efficacy in a prime vaccination regimen against wild-type (WT) A/Texas/37/2024 H5N1. The attenuation of LPhTXdNS1 in vitro was confirmed by its reduced replication in cultured cells and inability to control IFN{beta} promoter activation. In C57BL/6J mice, LPhTXdNS1 has reduced viral replication and pathogenicity compared to WT A/Texas/37/2024 H5N1. Notably, LPhTXdNS1 vaccinated mice exhibited high immunogenicity that reach its peak at weeks 3 and 4 post-immunization, leading to robust protection against subsequent lethal challenge with WT A/Texas/37/2024 H5N1. Altogether, we demonstrate that a single dose vaccination with LPhTXdNS1 is safe and able to induce protective immune responses against H5N1. Both safety profile and protection immunity suggest that LPhTXdNS1 holds promise as a potential solution to address the urgent need for an effective vaccine in the event of a pandemic for the treatment of infected animals and humans.

In the decade since the West African Ebola virus (EBOV) epidemic, several medical countermeasures against this often-fatal hemorrhagic disease have been approved by regulatory authorities for human use. This includes monoclonal antibody-based therapies and vaccines which have been stockpiled in limited quantities. One of the vaccines is based on vesicular stomatitis virus (VSV) expressing the EBOV glycoprotein (GP) as the immunogen. The vaccine is stockpiled in limited quantity for emergency use. A single high dose has been shown to rapidly protect humans within 10 days. We developed an updated version of this vaccine expressing the GP from the 2015 EBOV-Makona isolate. Here, we wanted to determine the protective efficacy within 10 days of a single moderate dose (10-fold and 1,000-fold dilution) of the updated vaccine in nonhuman primates (NHPs). As a comparator we included a 1000-fold dilution dose group of the approved vaccine expressing the EBOV-Kikwit GP. While we achieved uniform protection with the approved vaccine at the moderate dose, only 50% of the NHPs receiving the same dose of the updated vaccine expressing the EBOV-Makona GP were protected. This study highlights the importance of evaluating VSV-based vaccine stocks expressing different filovirus GPs in preclinical models prior to progression with clinical development. Our study also highlights that rapid vaccination with reduced doses still leads to protection but at the cost of "sterile" immunity raising concerns regarding EBOV persistence and potential downstream transmission. Therefore, lower vaccine doses should only be considered in cases of severe vaccine shortage.

BackgroundArmed conflict disrupts health systems, undermining routine immunization and disease surveillance. These disruptions can delay outbreak detection and allow population susceptibility to accumulate unnoticed. This study assessed the impact of the 2020 - 2022 conflict in Tigray, Ethiopia, on measles epidemiology, focusing on surveillance reporting, age distribution of cases, and vaccination status. MethodsWe conducted a retrospective longitudinal analysis of national case-based measles surveillance data from Ethiopia (2018-2024; n = 69,866). The study period was classified into pre-conflict (2018 - 2019), conflict peak (2020 - 2022), and post-conflict recovery (2023 - 2024) phases. Two-way analysis of variance examined regional differences in age at infection across phases. Multivariable logistic regression estimated adjusted odds ratios (aORs) for confirmed measles cases being unvaccinated (zero-dose), using the pre-conflict period as the reference and adjusting for age and sex. Surveillance quality was assessed using demographic data completeness. ResultsDuring the conflict peak, reported measles cases from Tigray declined to 0.01% of nationally reported cases, consistent with near-total surveillance collapse. After hostilities ended, a marked pediatric shift emerged, with the median age of infection in Tigray declining from 24.0 years during the conflict to 5.0 years in the post-conflict period (p < 0.0001), a pattern not observed in other regions. Compared with the pre-conflict baseline, the odds that a confirmed measles case was zero-dose were substantially higher during the conflict peak (aOR: 71.43; 95% CI: 14.1 - 1000.0) and remained elevated during post-conflict recovery (aOR: 2.49; 95% CI: 1.17 - 5.52). During the conflict peak, 50% of confirmed cases in Tigray lacked sex-disaggregated data. ConclusionThe conflict in Tigray severely disrupted immunization services and surveillance, delaying detection of a large susceptible pediatric cohort. These findings underscore the need for age-targeted catch-up vaccination and resilient surveillance systems during post-conflict recovery. Key questionsO_ST_ABSWhat is already known?C_ST_ABSO_LIArmed conflict disrupts routine immunization and increases the risk of measles outbreaks in low- and middle-income countries. C_LIO_LIConflict also weakens disease surveillance systems, which can delay outbreak detection and obscure the true burden of vaccine-preventable diseases. C_LIO_LIMeasles is highly sensitive to disruptions in vaccination coverage and is often among the first diseases to resurge following health system breakdown. C_LI What are the new findings?O_LIDuring the 2020-2022 conflict in Tigray, measles surveillance reporting declined to near zero, despite rising national measles incidence. C_LIO_LIAfter the cessation of hostilities, measles cases in Tigray shifted sharply toward young children, revealing a large cohort of unvaccinated children that had accumulated during the conflict period. C_LIO_LICompared with the pre-conflict period, confirmed measles cases in the post-conflict period had substantially higher odds of being zero-dose, indicating prolonged interruption of routine immunization services. C_LI What do the new findings imply?O_LISurveillance data from conflict-affected settings may substantially underestimate disease burden during periods of active conflict, leading to delayed recognition of outbreaks. C_LIO_LIPost-conflict recovery strategies should prioritize age-stratified catch-up vaccination campaigns targeting children born during conflict periods, rather than relying solely on routine immunization services. C_LIO_LIStrengthening surveillance resilience in fragile and conflict-affected settings is essential to prevent delayed detection of measles and other vaccine-preventable disease outbreaks. C_LI

Between 2022 and 2025, highly pathogenic avian influenza viruses (HPAIVs) of clade 2.3.4.4b, including four distinct H5 Eurasian (EA) genotypes, were detected in wild birds and mammals in the Svalbard Archipelago and on the island of Jan Mayen. We describe their epidemiology and genomic characteristics to improve understanding of HPAIV occurrence and transmission in the High Arctic. The initial cases in 2022 occurred during summer and involved a glaucous gull (Larus hyperboreus) and great skuas (Stercorarius skua) on Svalbard and Jan Mayen, representing the first detections of HPAIVs in the High Arctic. Three HPAIV genotypes were identified: EA-2020-C (H5N1), EA-2021-AB (H5N1), and EA-2021-I (H5N5). In 2023, HPAIVs were detected in a broader range of bird species, and retrospectively in an Atlantic walrus reported by another research group (Odobenus rosmarus rosmarus). Genotypes identified in 2023 were EA-2020-C (H5N1), EA-2021-I (H5N5), and EA-2022-BB (H5N1). No cases were reported in 2024. In 2025, EA-2021-I (H5N5) was detected in Arctic foxes (Vulpes lagopus) on Svalbard, without preceding detections in wild birds. The foxes exhibited neurological symptoms, and necropsy of one individual revealed the presence of feathers in its stomach. All sequenced viruses from the Arctic foxes uniquely carried the combination of PB2-E627K and PB1-H115Q, which is associated with mammalian adaptation. The detection of multiple genotypes indicates repeated and independent introductions of HPAIVs into these regions. The co-circulation of genetically distinct virus strains in areas of high bird density further suggests that Arctic breeding grounds may facilitate local viral amplification, reassortment, and subsequent dissemination along migratory flyways, including transcontinental spread. Data summaryThe authors confirm all supporting data, code and protocols have been provided within the article or through supplementary data files. Influenza A whole genome sequences generated through this study are available under the GISAID accession numbers found in Table 1. All genome sequences and associated metadata supporting the findings of this study can be accessed through the persistent digital object identifier https://doi.org/10.55876/gis8.260211rq. O_TBL View this table: org.highwire.dtl.DTLVardef@15e1921org.highwire.dtl.DTLVardef@c3e91borg.highwire.dtl.DTLVardef@1fcfe78org.highwire.dtl.DTLVardef@a69606org.highwire.dtl.DTLVardef@c36c74_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 1.C_FLOATNO O_TABLECAPTIONDetections of highly pathogenic avian influenza virus (HPAIV) in wild birds and mammals sampled in the Svalbard Archipelago and on Jan Mayen from January 1st, 2022, to August 31st, 2025. C_TABLECAPTION C_TBL

Zoos may serve as sentinel sites for zoonotic vector-borne diseases. West Nile virus (WNV) and Usutu virus (USUV) are closely related orthoflaviviruses transmitted between Culex mosquitoes and a bird reservoir. Both viruses can also infect mammals, including humans, where they may cause symptoms and, more rarely, hospitalization and death. However, serological cross-reactivity between WNV and USUV complicates their differential diagnosis. Here, we aimed to reconstruct the dynamics of emergence of WNV in a zoo located in a newly affected area in Europe, using ELISA and Virus Neutralization Test (VNT) serological analysis of 1707 animal sera collected between 2015 and 2024. Combining this data in a model accounting for cross-reactivity with USUV, we estimated yearly forces of infection (FOI) by both viruses, and thus found that WNV likely circulated in the area one year prior to the first cases reported to the passive surveillance system. Our results also showed that, in the zoo, mammals and reptiles had a lower risk of infection than birds (relative risk of 0.14 [0.05; 0.28]), and that the exposure of birds to water (aquatic lifestyle or proximity to stagnant water) affected the risk. Finally, we estimated diagnosis parameters, including the sensitivity of the VNT (80.4% [76.5%; 84.3%]), the expected VNT titer value, and the level of serological cross-reactivity between viruses during the VNT. To conclude, our modelling framework allowed to disentangle the co-circulation of two closely related viruses, a crucial point in ensuring the reliable sentinel surveillance of these vector-borne zoonotic pathogens.