#Human #infections with avian #influenza #H5 viruses with potential #pandemic #risk: 1997–2025

 

ABSTRACT

Highly pathogenic avian influenza (HPAI) A(H5) viruses have caused sporadic human infections since 1997, with recent detections in the Americas and Asia. However, the evolutionary dynamics of different HPAI A(H5) viruses at the animal–human interface, along with their associated disease severity, propensity for animal-to-human (zoonotic) spillover, and human-to-human transmission potential, remain unclear. Here, we combine available genetic and epidemiological data with mechanistic models to better understand the global spread of HPAI A(H5) viruses that spilled over to humans in 1997–2025. Analysis of 7445 subsampled hemagglutinin gene sequences revealed frequent regional succession of HPAI A(H5) virus clades that varied by geographic location. The 1104 reported human HPAI A(H5) cases exhibited subtype- and clade-specific heterogeneity in age, gender, and exposure sources (p < 0.001). After adjusting for under-reporting, we estimated case-fatality risk to be low for HPAI A(H5N1) clade 2.3.4.4b (0.7%, 95%CI: 0.02%–3.9%) and for A(H5N6) clades 2.3.4x (0%, 0%–1.1%) and 2.3.4.4b (1.6%, 0.7%–3.2%), compared with other A(H5) clades (range: 4.7%–15.0%). We also show that, while the transmissibility of HPAI A(H5) viruses between humans remains very low to date (mean Rt: 0.10–0.23), zoonotic transmission has increased with the emergence of bovine-origin clade 2.3.4.4b (incidence: 7.85 per million people per year), relative to other avian-origin A(H5) clades (range: 1.54–5.04 per million people per year). Although other factors such as exposure sources, routes of transmission, immune function, underlying medical conditions, and clinical management can influence outcomes of case-patients, these findings highlight the ongoing pandemic threat posed by HPAI A(H5) viruses and the need for ongoing comprehensive surveillance, genotypic and phenotypic characterization, and preparedness.

Source: 

Link: https://academic.oup.com/nsr/article/13/7/nwaf471/8317928

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Mechanistic #modelling of highly pathogenic avian #influenza: A scoping #review revealing critical gaps in cross-species #transmission models

 

Abstract

Background

Highly pathogenic avian influenza (HPAI) viruses, particularly subtypes such as H5N1 and H7N9, have caused widespread outbreaks in wild birds, poultry, livestock and occasionally humans, raising concerns about cross-species transmission and pandemic potential. Effective control and surveillance strategies require a thorough understanding of HPAI transmission dynamics, which can be supported by mathematical modelling.

Objective

This scoping review aimed to identify mechanistic models used to study HPAI transmission. Specifically, we sought to categorize model types, describe their application contexts (e.g., wild birds, poultry, livestock, and humans), and highlight modelling gaps relevant to understanding and mitigating the risks of HPAI spread.

Methods

Following PRISMA guidelines and the PRISMA extension for scoping reviews (PRISMA-ScR), we conducted systematic searches of PubMed and Web of Science to identify peer-reviewed studies employing deterministic and stochastic models to analyze HPAI transmission. Eligible articles published between January 2023 and June 2025 were screened and grouped by model structure, host populations, transmission pathways, and modelling objectives.

Results

After screening, 30 studies published after 2023 were included in this scoping review. Compartmental models were the most common (26 studies), with 16 deterministic and 10 stochastic approaches. These models were primarily used to describe transmission among wild birds, poultry, livestock, and humans and to evaluate interventions such as culling, vaccination, and movement restrictions. Agent-based models (2 studies) captured individual-level interactions and spatial heterogeneity, while network models (2 studies) represented contact structures and transmission pathways between farms or species.

Conclusions

Currently, mechanistic modelling of HPAI is dominated by compartmental approaches, including both deterministic and stochastic formulations, whereas agent-based and network models remain relatively underused. Although most studies focus on transmission in wild birds and poultry, and in some cases spillover infections to humans, few explicitly examine infection dynamics in livestock or in transmission between livestock and humans, despite the importance of livestock (e.g., cattle) as potential intermediaries in human infection. Key gaps persist in the integration of empirical data, representation of multi-host interactions, and evaluation of realistic intervention strategies. Addressing these limitations is essential to improve predictive accuracy and to strengthen the role of modelling in informing HPAI surveillance and control.

Source: 

Link: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0347929

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Seasonal forcing and waning #immunity drive the sub-annual periodicity of the #COVID19 #epidemic

 

Abstract

Seasonal trends in infectious diseases are shaped by climatic and social factors, with many respiratory viruses peaking in winter. However, the seasonality of COVID-19 remains in dispute, with significant waves of cases across the United States occurring in both winter and summer. Using wavelet analysis of COVID-19 cases during the pandemic period, we find that the periodicity of epidemic COVID-19 varies markedly across the U.S. and correlates with winter temperatures, indicating seasonal forcing. However, seasonal forcing alone cannot explain the pattern of multiple waves per year that has been so characteristic of COVID-19. Using a modified SIRS model that allows specification of the tempo of waning immunity, we show that specific forms of non-durable immunity can sufficiently explain the sub-annual waves characteristic of the COVID-19 epidemic.

Source: 

Link: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014169

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Using an evolutionary epidemiological #model of #pandemics to estimate the #infection #fatality ratio for #humans infected with avian #influenza viruses

 

Abstract

The risk of highly pathogenic avian influenza virus infection to humans is challenging to estimate as many human avian influenza virus (AIV) infections are undetected because infections may be asymptomatic, symptomatic but not tested, and difficult to identify through contact tracing, as human-to-human transmission is rare. We derive equations that consider the evolutionary mechanisms that give rise to pandemics and are parameterized to be consistent with records of past pandemics. We estimate that thousands of human AIV infections occur worldwide in an average year and estimate the infection fatality ratio as 32 deaths per 10,000 infections (95% confidence interval: [9.6, 75]). This estimate is comparable to SARS-CoV-2 during the recent pandemic and higher than seasonal human influenza. We estimate that preventing animal-to-human influenza spillovers would delay pandemic emergence by several years. Preventing human infections with AIV is necessary given the high risk of severe outcomes to individuals and to reduce the risk of pandemics occurring in the future.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

AH was supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant (RGPIN 023-05905) and a Catalyst Grant: Avian Influenza OneHealth Research, Enhanced tracking of the circulation of and risk from highly pathogenic avian influenza viruses at the human-wildlife interface from the Canadian Institutes of Health Research. JM, ML, and AH were support by an Atlantic Canada Research in the Mathematical Sciences Collaborative Research Group award.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.01.21.26344526v2

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Deep #disadvantage in #mortality on the frontlines of the #COVID19 #pandemic

 

Abstract

This study presents new evidence on the temporal and spatial impact of the COVID-19 pandemic on mortality among especially vulnerable New Yorkers. Using burial records from Hart Island—the City’s potter’s field—we study the distribution of unclaimed deaths over time and across boroughs in 2020 compared to pre-pandemic levels. We show that the Hart Island deaths began deviating from their historical pattern in early March 2020 and peaked five weeks later at 22 deaths for every death in the same week in 2019 (20:1 adjusted). COVID-19 excess death rates were more than twice as high in the Bronx compared to other boroughs. Citywide, we estimate that 10% of all COVID-related excess deaths during the initial outbreak (March–August 2020) were unclaimed. These findings suggest the pandemic greatly magnified existing inequalities in the City and, more broadly, illustrate the especially devastating impact of COVID-19 on economically and socially vulnerable populations.

Source: 

Link: https://www.nature.com/articles/s41598-026-41219-6

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#Genomic analysis of high pathogenicity avian #influenza viruses from #Antarctica reveals multiple introductions from South #America

 

Abstract

The spread of high pathogenic avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b into Antarctica poses a major threat to polar wildlife. We report the detection of H5N1 in carcasses of eight species during the 2023-2024 and 2024-2025 austral summers in the South Shetland Islands: Antarctic shag, Antarctic tern, kelp gull, pintado petrel, Antarctic petrel, skuas, Antarctic fur seal, and southern elephant seal. Whole-genome sequencing, mutational profiling, and phylogenetic reconstruction revealed that the viruses detected in these hosts descended from distinct introduction events. One group of strains including complete and partial viral genomes from a gull, skuas, fur seals, an Antarctic tern, and a southern elephant seal clustered with H5N1 strains previously detected in marine mammals in South America and formed a polyphyletic lineage consistent with at least two independent introductions into Antarctica. A second group of strains including complete and partial viral genomes from petrels, shags, and skuas clustered with H5N1 strains previously detected in seabirds and marine mammals in South Georgia and with a previously reported HPAIV detection from Torgersen Island, Antarctic Peninsula. These findings reveal extensive epidemiological connectivity between South America and Antarctica, with South Georgia serving as a “stepping stone” for virus spread in the region.

Source: 

Link: https://www.nature.com/articles/s41467-026-71544-3

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#Oropouche virus #outbreaks in northeast #Brazil between 2024–25 are characterized by sustained #transmission and spread to newly affected areas

 

Abstract

Oropouche virus (OROV) has recently expanded in Brazil, establishing transmission in non-endemic regions. This study aims to integrate epidemiological and molecular data to investigate OROV spread in Northeast (NE) Brazil between 2024 and 2025. OROV cases were analyzed regarding ecological risk factors and geographical clustering. Additionally, we sequenced 65 new OROV genomes from the Northeast states of Pernambuco, Paraíba, and Sergipe to infer the virus’s spatiotemporal dynamics in NE Brazil. A total of 2,806 confirmed cases were reported between March 2024 and April 2025, affecting 170 municipalities across eight out of nine NE states, with highly heterogeneous incidence. An ecological shift was observed, with OROV transmission moving from Atlantic Forest areas in 2024 to humid Caatinga zones in 2025. Phylogenetic reconstruction revealed multiple independent viral introductions in Northeast in 2024, including two in Pernambuco. The first, originating from the central Amazonas, became the main driver of local transmission and subsequently spread to Sergipe and Paraíba, causing outbreaks in 2024 and 2025, respectively. The second introduction remained restricted within Pernambuco. While several Northeast municipalities reported high OROV incidence, Jaqueira (Pernambuco) emerged as a key hub for regional viral spread. OROV showed sustained transmission in the region over a two-year period, characterized by marked spatiotemporal displacement consistent with short-lived, rapidly spreading outbreaks, followed by cryptic transmission and subsequent dissemination to new areas, ultimately driving renewed intense outbreaks.

Source: 

Link: https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014171

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Dynamics and #control of highly pathogenic #H5 avian #influenza in a threatened #pelican population

 

Abstract

The ongoing epizootic of highly pathogenic avian influenza (HPAI) continues to cause massive deaths in wildlife. Fundamental understanding of its disease ecology in natural populations is urgently needed. This knowledge has been hindered by the difficulty of acquiring data on epidemic dynamics. Here, using data collected from a threatened population of Dalmatian pelicans (Pelecanus crispus), we recover the epidemiological and evolutionary history of one of the largest HPAI wildlife mortality events. The results show that this devastating outbreak was likely seeded by a single introduction associated with movement of the species. By estimating epidemiological features of two consecutive outbreaks in the same population, we show that panzootic H5N1 since 2022 likely exhibits higher transmissibility and longer shedding time in non-reservoir birds, compared to previous H5NX subtypes. We also evaluate effectiveness of past and future control measures: carcass removal during the outbreak is shown to have surprisingly little impact on mitigating the mortality; and current H5 vaccines relying on capture and injection to deliver cannot establish herd immunity in a wildlife population. The results provide the first field evidence supporting the hypothesis that viral fitness difference of H5N1 to previous H5NX subtypes is the key cause of the expanded epizootic and panzootic since 2022, and on highly debated HPAI management strategies in wildlife populations.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.03.16.712014v1

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Case presentation of #patients hospitalised with #mpox (subclade Ib/2023sh) including #children, #adolescents, and #adults in South Kivu, #DRC: an observational cohort study

 

Summary

Background

Mpox is a public health concern in eastern DR Congo. It continues to cause substantial numbers of hospital admissions, with changing demographics including children and adolescents, requiring comprehensive clinical and epidemiological investigation. In this study, we aim to describe the clinical characteristics of hospitalised participants infected with monkeypox virus (MPXV) subclade Ib/2023sh in the Kabare Territory in South Kivu, DR Congo.

Methods

This observational cohort study included patients admitted with suspected mpox to the reference centre of mpox treatment at Lwiro Hospital, South Kivu, DR Congo. Eligible participants must have had, at the time of inclusion, skin lesions compatible with the infection. Individuals who did not present lesions compatible with MPXV infection were also eligible if they had at least one of the following symptoms: fever, cervical lymphadenopathy, or pharyngitis, provided they had been in contact with someone with suspected mpox within the last 21 days. Data from hospital records and standardised clinical forms captured demographics, presenting symptoms and signs, outcomes, and general clinical characteristics. Descriptive analyses and statistics summarised the clinical and epidemiological profiles of participants with molecular confirmation of MPXV subclade Ib/2023sh.

Findings

Between Aug 3, 2024, and Feb 8, 2025, MPXV subclade Ib/2023sh was detected in 494 (77%) of 643 participants with a median age of 9 years (IQR 2–24). Participants who were positive for MPXV subclade Ib/2023sh infection were more often female (290 [59%]) and were generally older (median 16 years [4–25]) than male participants (204 [41%]; median age 4 years [1–14]). 300 (61%) of 494 participants were aged 15 years or younger. Fever (444 [90%]), skin lesions or rash (391 [79%]), and dysphagia (279 [56%]) were the most prevalent symptoms. Children aged 0–5 years had a higher frequency of lesions on the head (84 [41%] of 203), face (67 [33%]), neck (23 [11%]), back (27 [13%]), arm (35 [17%]), palm of hand (35 [17%]), chest (46 [23%]), posterior aspect of thighs (40 [20%]), legs (25 [12%]), dorsal foot (45 [22%]), and oral cavity (37 [18%]). 117 (24%) participants had lesions in the oral cavity. Oral cavity and oropharynx swabs were able to detect MPXV subclade Ib/2023sh in the absence of assayable skin lesions.

Interpretation

The high proportion of children and adolescents (aged ≤15 years) differentiates our cohort from other clinical descriptions of the novel MPXV subclade Ib/2023sh. Given that, we hypothesise a demographic shift in the target population that contributes to the community spread of mpox in the South Kivu region of DR Congo. Targeted public health measures should consider ways to reduce transmission among children and adolescents.

Funding

Canadian Institutes of Health Research (CIHR), Canadian Foundation for Innovation, Research Nova Scotia, Dalhousie Medical Foundation, Moderna, Li-Ka Shing Foundation, European & Developing Countries Clinical Trials Partnership (EDCTP).

Translations

For the French, Swahili and Mashi translations of the abstract see Supplementary Materials section.

Source: 

Link: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(26)00051-4/fulltext?rss=yes

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Spatiotemporal #clustering of highly pathogenic avian #influenza (HPAI) #H5N1 at the wild #waterfowl - #poultry interface: Vector-specific #spillover risks in the #US, 2022–2025

 

Abstract

Background: 

The 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 understand and mitigate this risk. 

Methods: 

Publicly 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. 

Results: 

A 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. 

Conclusions: 

The 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.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.03.06.710020v1

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Adult #obesity and #risk of severe #infections: a multicohort study with global burden estimates

 

Summary

Background

Adult obesity has been linked to specific infections, but evidence across the full spectrum of infectious diseases remains scarce. In this multicohort study with impact modelling, we examined the association between this preventable risk factor and the incidence, hospitalisations, and mortality of 925 bacterial, viral, parasitic, and fungal infectious diseases, and estimated their global and regional attributable impact.

Methods

We used pooled data from two Finnish cohort studies and repeated analyses in an independent population from the UK Biobank. BMI was assessed at baseline (1998–2002 in the Finnish studies; 2006–10 in UK Biobank), and participants were categorised as having healthy weight (18·5–24·9 kg/m2), overweight (25·0–29·9 kg/m2) or obesity, classified as class I (30·0–34·9 kg/m2), class II (35·0–39·9 kg/m2), or class III (≥40·0 kg/m2). Participants were followed up through national hospitalisation and mortality registries for hospital admissions and deaths due to infectious diseases. Using hazard ratios derived from the Finnish cohorts and UK Biobank, along with obesity prevalence estimates from the Global Burden of Diseases, Injuries, and Risk Factors Study database, we estimated the proportion of fatal infections attributable to obesity globally, regionally, and by country for the years 2018 (before), 2021 (during), and 2023 (after the COVID-19 pandemic).

Findings

The analysis included 67 766 adults (mean age 42·1 [SD 10·8] years; 49 516 [73·1%] females, 18 250 [26·9%] males) from the Finnish cohorts and 479 498 adults (mean age 57·0 [SD 8·1] years; 261 084 [54·4%] females, 218 414 [45·6%] males) from UK Biobank. Participants had no recent history of infection-related hospitalisations at baseline. During follow-up, there were 8230 incident infection cases in the Finnish cohorts and 81 945 in UK Biobank. Compared with individuals of healthy weight, those with class III obesity had a three-times higher risk of infection-related hospital admissions (Finnish cohorts 2·75 [95% CI 2·24–3·37], UK Biobank 3·07 [2·95–3·19]), death (Finnish cohorts 3·06 [1·25–7·49], UK Biobank 3·54 [3·15–3·98]), or either outcome (Finnish cohorts 2·69 [2·19–3·30], UK Biobank 3·07 [2·95–3·19]). The corresponding pooled hazard ratio for either fatal or non-fatal severe infection among individuals with any obesity (classes I–III) was 1·7 (1·7–1·8). This association was consistent across different indicators of obesity (BMI, waist circumference, and waist-to-height ratio), demographic and clinical subgroups, and a wide range of infections (non-fatal and fatal, acute and chronic, bacterial and viral [including subtypes], and parasitic and fungal). Applying these risk estimates to global burden of disease data, the population attributable fractions of infection-related deaths due to obesity were estimated at 8·6% (6·6–11·1) in 2018, 15·0% (12·8–17·4) in 2021, and 10·8% (8·6–13·6) in 2023.

Interpretation

Adult obesity is a risk factor for infection-related hospitalisations and mortality across diverse pathogen types, populations, and baseline clinical profiles, with evidence suggesting that approximately one in ten infection-related deaths worldwide might be attributable to obesity.

Funding

Wellcome Trust, Medical Research Council, and Research Council of Finland.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S0140673625024742?dgcid=rss_sd_all

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Characteristics and #Transmission Dynamics of Global #Travel-Related #Mpox Cases Caused by Clade Ib Monkeypox Virus

 

Abstract

We examined 89 travel-related clade Ib monkeypox virus cases detected in 33 countries during August 2024–July 2025. Most cases were among men; about one third led to secondary transmission. Secondary transmission risk was highest among sexual, then household, contacts. Those groups should be the focus of response strategies and interventions.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/2/25-1530_article

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The effect of #NPIs on #influenza throughout the #COVID19 #pandemic: an 8-year interrupted time series study

 

Abstract

Limited information is available on the impact of non-pharmaceutical interventions (NPIs) and immune debt on influenza during COVID-19. This retrospective population-based research examined the effect of the COVID-19 pandemic on the prevalence of influenza-like illness (ILI) cases and influenza positive cases in Sichuan Province. Interrupted time series analysis (ITS) was conducted using data gathered from surveillance hospitals throughout 21 cities, including information on patients diagnosed with ILI and positive nucleic acid testing. Subsequent to the implementation of NPIs, there was a notable temporary reduction in both the incidence of ILI cases and confirmed influenza cases, decreasing by 94.7% and 98.0%, respectively (P<0.001). The weekly trend in influenza-positive cases was notable (+4.1%/week, P=0.001). Following the execution of the second-phase intervention, the fluctuations in the transient changes of ILI patients and influenza-positive cases varied; nonetheless, both subsequently exhibited a significant declining trend (P<0.001). Temperature had a substantial negative correlation with both indicators (P<0.001), resulting in a reduction of instances by 13.0% and 11.5%, respectively; humidity demonstrated no statistically significant impact on either. Our data demonstrate that NPIs significantly reduce two influenza outcome indicators in the short term; nevertheless, they do not effectuate a sustainable alteration in the long-term increasing trend of influenza. Through the examination of the dynamic effects of NPIs on influenza transmission, we provide policymakers with an enhanced evaluative instrument, a decision-making framework, and theoretical backing, while also contemplating the prospective advantages and hazards of NPIs for additional respiratory infectious diseases in the future.

Source: 

Link: https://www.nature.com/articles/s41598-026-37911-2

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Subclade K #influenza A #H3N2 viruses display partial immune #escape with preserved cross-neutralisation in a #UK population

 

Abstract

We examined whether the recent emergence of influenza A(H3N2) subclade K, associated with an unusually early influenza season in the Northern hemisphere, was accompanied by a reduction in human population immunity. Using virus neutralisation assays on pre-epidemic human sera collected in May 2025, we found evidence of moderate antigenic drift. Further, vaccines used in the 2024/2025 season induced cross-neutralising immunity. These findings provide timely insight for interpreting recent influenza epidemiology and informing vaccine strain selection.

Competing Interest Statement

The following authors declare no conflict of interests: KD, RI, LM, SR, HC, GGA, MSA, VS, ZW, SKW, JZ, BJW, DLR, JH, OML, JG, CJRI. PRM receives funding for research work for MSD. EH has received an honorarium for advisory board work for Seqirus. ET has received funding from Novavax and Astra Zeneca.

Funding Statement

This work was funded by the Medical Research Council (MRC) to the MRC-University of Glasgow Centre for Virus Research (grants MC_UU_0034/1, MC_UU_0034/2, MC_UU0034/3, MC_UU0034/5 and MC_UU0034/6). Funding to EH and PRM from the Medical Research Council (MRC) and Department for Environment, Food and Rural Affairs (Defra, UK) as FluTrailMap-One Health [MR/Y03368X/1] is also acknowledged.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.01.27.26344933v1

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Increased #Mortality Rates During the 2025 #Chikungunya #Epidemic in #Réunion Island

 

Abstract

Background: 

Chikungunya virus (CHIKV) has historically been regarded as a low-fatality infection; however, growing evidence from diverse study designs demonstrated a substantial mortality burden during large-scale epidemics. In 2025, Réunion Island experienced a major CHIKV outbreak, raising renewed concerns about its fatal impact. 

Methods: 

We conducted an ecological time-series analysis of all-cause mortality during the 2025 chikungunya epidemic. Expected deaths were estimated using two complementary approaches: (i) a baseline based on age-specific mean mortality rates from the same calendar months in the post-pandemic period and (ii) long-term Poisson regression models using a log-link function and population offset, excluding the COVID-19 pandemic period. Excess mortality was calculated as the difference between observed and expected deaths during periods when observed mortality significantly exceeded the upper bound of the 95% confidence interval. 

Results: 

Observed mortality exceeded the upper 95% confidence interval (CI) limit for three consecutive months, coinciding with the epidemic curve and resulting in an estimated 208 excess deaths. These deaths were concentrated among older adults, peaking in April 2025 with a mortality rate ratio of 1.34 (95% CI: 1.22–1.47; p < 0.001). Among older adults, the age-specific excess mortality rate reached 145.3 per 100,000 (95% CI: 125.5–165.0) with a case fatality rate (CFR) of 2.4%, resulting in an overall population excess mortality rate of 23.2 per 100,000 and a total CFR of 0.4%. The number of deaths identified through routine surveillance was substantially lower than our estimates, highlighting a significant discrepancy between reported and excess chikungunya-associated mortality. 

Conclusions: 

Chikungunya epidemics are consistently associated with substantial underrecognized mortality worldwide. Routine surveillance relying solely on laboratory confirmation underestimates the true burden of the disease. Integrating excess mortality analysis, strengthening diagnostic and postmortem investigations, and implementing timely mitigation measures are essential to accurately assess and reduce preventable deaths during future CHIKV outbreaks.

Source: 

Link: https://www.mdpi.com/1999-4915/18/2/180

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Using an evolutionary #epidemiological #model of #pandemics to estimate the #infection #fatality ratio for #humans infected with avian #influenza viruses

 

Abstract

The risk of highly pathogenic avian influenza infection to humans is challenging to estimate because many human avian influenza virus (AIV) infections are undetected as they may be asymptomatic, symptomatic but not tested, and as contact tracing is difficult because human-to-human spread is rare. We derive equations that consider the evolutionary mechanisms that give rise to pandemics and are parameterized to be consistent with records of past pandemics. We estimate that thousands of human AIV infections occur worldwide in an average year and estimate the infection fatality ratio as 32 deaths per 10,000 infections (95% confidence interval: [9.6, 75]). We estimate that preventing 20% of animal-to-human influenza spillovers annually would delay pandemic emergence by an average of 9.4 years. There is a high level of uncertainty in our estimates due to the few records of past pandemics, but even so this infection fatality ratio is comparable to SARS-CoV-2 during the recent pandemic and is higher than seasonal human influenza. Preventing human infections with AIV is necessary given the high risk of severe outcomes to individuals and to reduce the risk of pandemics occurring in the future.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

AH was supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant (RGPIN 023-05905) and a Catalyst Grant: Avian Influenza OneHealth Research, Enhanced tracking of the circulation of and risk from highly pathogenic avian influenza viruses at the human-wildlife interface from the Canadian Institutes of Health Research. JM, ML, and AH were support by an Atlantic Canada Research in the Mathematical Sciences Collaborative Research Group award.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.01.21.26344526v1

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Modeling of #H5N1 #influenza virus #kinetics during dairy #cattle #infection suggests the timing of infectiousness

 

Abstract

Since early-2024 unprecedented outbreaks of highly pathogenic avian influenza H5N1 clade 2.3.4.4b have been ongoing in dairy cattle in the United States with significant consequences for the dairy industry and public health. Estimation of key epidemiological parameters is required to support outbreak response, including predicting the likely effectiveness of interventions and testing strategies. Here, we pool limited publicly available data from four studies of naturally and experimentally infected dairy cattle. We quantify Ct value trajectories of infected dairy cattle and the relationship between Ct value and the log-titer of infectious virus, a proxy for infectiousness. We estimate that following infection minimum Ct values are rapidly reached within 1–2 days with a population mean Ct value of 15.7 (12.9, 18.4). We identify a threshold Ct value of 21.8 (19.9, 24.6), with values of Ct value above this threshold representing little-to-no infectious viral load. Finally, assuming a direct relationship between Ct value and infectiousness, we estimate the distribution of the duration of infectiousness for dairy cattle (i.e., the duration their Ct value remains below the critical threshold) with a population median of 7.8 (4.1, 13.9) days. Our estimates will be critical inputs to the development of outbreak management guidelines and modeling analyses informing response strategies.

Source: 

Link: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003586

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#Lassa fever #symptomatology, viral dynamics, and host immune response (PREPARE): a prospective, observational cohort study in #Liberia

 

Summary

Background

Lassa virus (LASV) is a persistent threat to public health in west Africa and beyond. LASV is endemic in west Africa and each year it is responsible for an estimated 2·7 million infections, 23 700 hospitalisations, and 5000 deaths. With over 32 reported cases of Lassa fever imported into non-endemic countries—one-third of which were fatal—the importance of enhanced detection and management of Lassa fever extends beyond west Africa.

Methods

The prevalence, pathogenesis, and persistence (PREPARE) study was a prospective cohort study among patients admitted to two hospitals in a hyperendemic area of Liberia. Any patients aged 5 years or older with a febrile illness were eligible to enrol and be tested for Lassa fever. The study aimed to measure the prevalence of LASV infection and assess the signs and symptoms, LASV viral replication kinetics, and LASV-specific IgM and IgG responses longitudinally among adults and children with laboratory-confirmed Lassa fever.

Findings

From July 10, 2018, to Aug 12, 2024, a total of 435 participants were enrolled, including 362 admitted with a febrile illness and 73 who were directly admitted with clinical suspicion for Lassa fever. Lassa fever was diagnosed by plasma LASV RT-PCR in 41 (11%) of 362 febrile participants and 47 (64%) of 73 participants directly admitted with suspected Lassa fever, resulting in a total of 88 cases of confirmed Lassa fever. At entry, anorexia (71 [81%] of 88 vs 178 [51%] of 347), severe fatigue or weakness (63 [72%] vs 178 [51%]), and nausea or vomiting (39 [44%] vs 95 [27%]) were more likely to be reported by participants with Lassa fever than by participants who tested LASV RNA negative. Among the participants with Lassa fever, 11 (13%) of 88 died after admission. Mental status changes, seizures, acute kidney failure, hyperkalaemia, and metabolic acidosis were more frequent in patients with Lassa fever who died than in patients who survived. Median cycle threshold values at study entry for glycoprotein complex gene (GPC) or polymerase gene (L) were lower in those who died (GPC cycle threshold 22·4 [IQR 20·0–27·9]; L cycle threshold 21·7 [19·0–27·7]) than in those who survived (GPC cycle threshold 31·5 [28·0–33·9]; L cycle threshold 32·3 [28·0–33·9]). Among the 70 participants with Lassa fever who consented to longitudinal follow-up through their hospitalisation, seven died and these participants tended to have lower cycle threshold values and lower IgM and IgG LASV responses compared with survivors.

Interpretation

In a region of Liberia where it is endemic, Lassa fever is a prevalent cause of morbidity and mortality. Several symptoms were more likely in those with Lassa fever but overlap with those caused by other common infectious diseases. Compared with survivors, those who died during hospitalisation for Lassa fever tended to have evidence of organ dysfunction along with higher viral loads at study entry and during follow-up and lower antibody levels during their illness, suggesting a muted humoral immune response might be a factor in the development of severe Lassa fever.

Funding

US National Institute of Allergy and Infectious Diseases and National Institutes of Health.

Source: 

Link: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(25)00725-X/abstract?rss=yes

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The #global, regional, and national burden of #cancer, 1990–2023, with #forecasts to 2050: a systematic analysis for the Global Burden of Disease Study 2023

 

Summary

Background

Cancer is a leading cause of death globally. Accurate cancer burden information is crucial for policy planning, but many countries do not have up-to-date cancer surveillance data. To inform global cancer-control efforts, we used the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2023 framework to generate and analyse estimates of cancer burden for 47 cancer types or groupings by age, sex, and 204 countries and territories from 1990 to 2023, cancer burden attributable to selected risk factors from 1990 to 2023, and forecasted cancer burden up to 2050.

Methods

Cancer estimation in GBD 2023 used data from population-based cancer registration systems, vital registration systems, and verbal autopsies. Cancer mortality was estimated using ensemble models, with incidence informed by mortality estimates and mortality-to-incidence ratios (MIRs). Prevalence estimates were generated from modelled survival estimates, then multiplied by disability weights to estimate years lived with disability (YLDs). Years of life lost (YLLs) were estimated by multiplying age-specific cancer deaths by the GBD standard life expectancy at the age of death. Disability-adjusted life-years (DALYs) were calculated as the sum of YLLs and YLDs. We used the GBD 2023 comparative risk assessment framework to estimate cancer burden attributable to 44 behavioural, environmental and occupational, and metabolic risk factors. To forecast cancer burden from 2024 to 2050, we used the GBD 2023 forecasting framework, which included forecasts of relevant risk factor exposures and used Socio-demographic Index as a covariate for forecasting the proportion of each cancer not affected by these risk factors. Progress towards the UN Sustainable Development Goal (SDG) target 3.4 aim to reduce non-communicable disease mortality by a third between 2015 and 2030 was estimated for cancer.

Findings

In 2023, excluding non-melanoma skin cancers, there were 18·5 million (95% uncertainty interval 16·4 to 20·7) incident cases of cancer and 10·4 million (9·65 to 10·9) deaths, contributing to 271 million (255 to 285) DALYs globally. Of these, 57·9% (56·1 to 59·8) of incident cases and 65·8% (64·3 to 67·6) of cancer deaths occurred in low-income to upper-middle-income countries based on World Bank income group classifications. Cancer was the second leading cause of deaths globally in 2023 after cardiovascular diseases. There were 4·33 million (3·85 to 4·78) risk-attributable cancer deaths globally in 2023, comprising 41·7% (37·8 to 45·4) of all cancer deaths. Risk-attributable cancer deaths increased by 72·3% (57·1 to 86·8) from 1990 to 2023, whereas overall global cancer deaths increased by 74·3% (62·2 to 86·2) over the same period. The reference forecasts (the most likely future) estimate that in 2050 there will be 30·5 million (22·9 to 38·9) cases and 18·6 million (15·6 to 21·5) deaths from cancer globally, 60·7% (41·9 to 80·6) and 74·5% (50·1 to 104·2) increases from 2024, respectively. These forecasted increases in deaths are greater in low-income and middle-income countries (90·6% [61·0 to 127·0]) compared with high-income countries (42·8% [28·3 to 58·6]). Most of these increases are likely due to demographic changes, as age-standardised death rates are forecast to change by –5·6% (–12·8 to 4·6) between 2024 and 2050 globally. Between 2015 and 2030, the probability of dying due to cancer between the ages of 30 years and 70 years was forecasted to have a relative decrease of 6·5% (3·2 to 10·3).

Interpretation

Cancer is a major contributor to global disease burden, with increasing numbers of cases and deaths forecasted up to 2050 and a disproportionate growth in burden in countries with scarce resources. The decline in age-standardised mortality rates from cancer is encouraging but insufficient to meet the SDG target set for 2030. Effectively and sustainably addressing cancer burden globally will require comprehensive national and international efforts that consider health systems and context in the development and implementation of cancer-control strategies across the continuum of prevention, diagnosis, and treatment.

Funding

Gates Foundation, St Jude Children's Research Hospital, and St Baldrick's Foundation.

Source: The Lancet, https://www.sciencedirect.com/science/article/abs/pii/S0140673625016356?dgcid=rss_sd_all

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#Global #epidemiology and public health #challenges of #MERS #Coronavirus

 

Highlights

• Middle East respiratory syndrome-coronavirus was first detected in 2012 in Saudi Arabia.

• Since 2012, Middle East respiratory syndrome caused 2626 confirmed cases.

• 20% of cases involve contact with dromedary camels or their products.

• Human-to-human spread occurs, mainly in healthcare settings.

• A case fatality rate is 36-40%.

Source: IJID Regions, https://www.sciencedirect.com/science/article/pii/S2772707625001663?via%3Dihub

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