Sex differences in #vaccine-induced #neuraminidase cross-recognition and #protection against #H5N1 in mice

 

Abstract

Despite concerns about the spread and pandemic potential of H5N1, there is no commercial H5N1 vaccine. Seasonal influenza vaccines offer some cross-protection against H5N1, but to date there has been no consideration of whether protection differs between the sexes. We investigated immune responses and protection in adult male and female C57BL/6 mice following vaccination with either inactivated H1N1 or H5N1 (LAIV backbone) virus vaccines. Vaccination induced strong homologous antibody responses, with females generating greater total IgG than males against both H1N1 and H5N1 vaccine, which was primarily mediated by greater IgG responses to neuraminidase (NA) than hemagglutinin (HA) protein. IgG cross-recognition of H1N1 also was greater among H5N1 vaccinated females and was primarily caused by greater IgG responses to N1. IgG2b and IgG2c were the primary isotypes generated in response to these vaccines, with females having greater IgG2b responses and greater binding to FcγRIV for avian and human NA than males in response to both homologous and heterologous vaccination. Antibody-dependent complement deposition was measured as an FcR-mediated non-neutralizing response against HA and NA and was robust in both sexes. Vaccinated females had greater neutralizing antibody titers than males against the homologous vaccine virus, with limited cross-neutralizing antibodies detected in either sexes. Neuraminidase inhibition titers were greater in vaccinated females than males against the heterologous virus following H1N1 vaccination and against both the vaccine and heterologous viruses following H5N1 vaccination. When H1N1 and H5N1 vaccinated mice were challenged with a lethal dose of A/Texas/37/2024 H5N1, all H5N1 vaccinated mice were protected, regardless of sex. Among H1N1 vaccinated mice, while both sexes were protected against disease, H1N1 vaccinated females cleared virus faster than their male counterparts. These findings highlight that female-biased NA-specific antibodies result in greater cross-protection and should be considered in studies of influenza vaccines.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

NIH/NIAID Johns Hopkins Center of Excellence for Influenza Research and Response, 75N93021C00045

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.26.728011v1

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Meeting of the #SAGE on #Immunization, March 2026: conclusions and recommendations {#COVID19 vaccines safety portion} (WHO, May 29 '26)

 

(...)

COVID-19 

    SAGE reviewed the latest epidemiological data on COVID-19 during the Omicron era, including the disease burden and post-COVID conditions, across population groups. 

    Evidence on the status of vaccine use globally and the safety, effectiveness and cost–effectiveness of currently available vaccines was also reviewed. 

    The global burden of severe COVID-19 has declined compared with earlier phases during the pandemic, largely due to widespread population immunity through vaccination and prior infection. 

    Nevertheless, COVID-19 continues to cause morbidity and mortality, particularly among older adults, individuals with comorbidities and people who are immunocompromised. 

    In terms of post-COVID-19 conditions, persistent symptoms following acute infection have been documented in both adults and children, although estimates of prevalence vary considerably across studies owing to differences in case definitions and study methods. 

    Vaccination may contribute to reducing the risk of post-COVID-19 conditions, primarily through prevention of severe disease. 

    In terms of the burden of COVID-19 during pregnancy and infancy in the Omicron era, the risk of severe disease and adverse maternal and fetal outcomes was lower than during the pandemic. 

    However, people who are pregnant remain at higher risk of severe disease in the Omicron era compared with those of a similar age who are not pregnant. 

    Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during pregnancy has been associated with an increased risk of adverse maternal outcomes (e.g. intensive care unit admission) and pregnancy outcomes (e.g. preterm birth). 

    Data on infants infected with SARS-CoV-2, which are mainly from a few high-income settings, indicate that infants aged under 6 months may experience higher hospitalization rates than older children, although the frequency of severe outcomes is low and varies within these settings. 

    The currently available mRNA and protein subunit COVID-19 vaccines have an acceptable safety profile across age groups and risk categories, based on 5 years of accumulated COVID-19 vaccine safety data from clinical trials, post-marketing pharmacovigilance systems, surveillance platforms, post-authorization studies and international regulatory reviews. 

    Serious adverse events remain rare relative to the number of doses administered globally (>13 billion); also, most reported adverse events are mild or moderate and transient, typically resolving within a few days. 

    A limited number of rare, platform-specific adverse events have been identified, including thrombosis with thrombocytopenia syndrome (TTS) associated with adenovirus vector vaccines that are no longer being manufactured, and myocarditis/pericarditis associated with mRNA and protein vaccines. 

    However, myocarditis and pericarditis associated with the currently available mRNA and protein vaccines remain uncommon, and have a milder course than post-COVID or conventional myocarditis; hence, the overall benefit–risk balance continues to favour vaccination, particularly among populations at increased risk of serious COVID-19 outcomes. 

    Safety following repeated doses, including revaccination with variant-adapted vaccines, remains reassuring, with no new safety signals identified.{24} 

    Real-world evidence consistently shows that the vaccines are effective in reducing COVID-19 associated severe disease and death. 

    Vaccines adapted to Omicron lineages continue to provide meaningful protection against severe outcomes. 

    Routine periodic COVID-19 vaccine doses help to sustain protection, despite the relatively rapid waning of protection against infection and limited protection against symptomatic disease beyond 6 months. 

    Updated evidence on COVID-19 vaccination during pregnancy from observational studies, pregnancy registries, and surveillance systems across multiple countries has not identified safety concerns. 

    Currently it shows no increased risk of adverse maternal or pregnancy-related outcomes, including miscarriage, stillbirth, preterm birth or adverse outcomes in infants born to people vaccinated during pregnancy. 

    Vaccination during pregnancy is safe and it provides protection to the pregnant individual, against COVID-19 associated adverse pregnancy outcomes, and to infants aged under 6 months through maternal antibody transfer. 

    Cost–effectiveness analyses of COVID-19 vaccination consistently show that programmes targeting populations at high risk of severe outcomes (e.g. older adults or individuals with underlying health conditions) are generally cost-effective or even cost saving across a range of epidemiological scenarios. 

    Broader vaccination strategies may be cost-effective in certain contexts, depending on disease burden, vaccine costs and programmatic factors. 

    Most studies originate from high-income countries, limiting their generalizability to other settings.

    SAGE recommended that countries should consider routine COVID-19 vaccination for those groups at highest risk of severe COVID-19 disease. 

    These include oldest adults;{25}  older adults{26} with significant comorbidities or severe obesity; residents in care and long-term care facilities; and individuals aged 6 months or over, who are moderately or severely immunocompromised. 

    For these groups – whether they are unvaccinated or were vaccinated more than 6 months earlier – SAGE recommended at least one dose per year, and preferably two doses administered 6 months apart, owing to the waning of protection against severe COVID-19 disease by 6 months after the last dose. 

    Cost–effectiveness and programmatic feasibility should be considered when determining the number of doses to be administered per year.  

    SAGE also recommended that countries may consider routine COVID-19 vaccination of additional groups based on local context, cost–effectiveness and programmatic feasibility. 

    These additional groups include the following: 

        • Older adults without significant comorbidities or severe obesity; adults (not included in the older adult category), adolescents and children with significant comorbidities or severe obesity; and health workers and other care providers. These groups, whether unvaccinated or previously vaccinated more than 6 months earlier, may be vaccinated with at least one dose per year. 

        • People who are pregnant, whether unvaccinated or previously vaccinated more than 6 months earlier. This group may be vaccinated with one COVID-19 vaccine dose during each pregnancy, at any stage, though ideally during the second trimester. The aim is to optimize protection against severe COVID-19 for the pregnant person, prevent adverse pregnancy outcomes and protect the infant during the first months of life. 

        • Previously unvaccinated healthy children aged 6–23 months. This age group may be vaccinated if a significant burden is documented; revaccination is not routinely recommended. 

    Some of the research priorities recommended by SAGE were further assessment of the burden, societal impact and vaccine effectiveness against post-COVID-19 condition, using the WHO standardized definition;{27}  studies on cost–effectiveness of COVID-19 vaccination, particularly in low- and middle-income countries, and among groups such as health workers and children; and studies on the social and behavioural drivers of COVID-19 vaccine uptake, to address hesitancy and guide interventions to achieve high confidence and uptake. 

    SAGE recommendations will inform the development of a WHO vaccine position paper on COVID-19 vaccines; the position paper will replace the WHO SAGE interim guidance reflected in the COVID-19 vaccines roadmap.{28} 

(...)

___

{24}   World Health Organization (2026). Global Advisory Committee on Vaccine Safety (GACVS): COVID-19 vaccines – Subcommittee. Geneva: WHO; [cited 2026 Mar 10]. Available from: https://www.who.int/groups/global-advisory-committee-on-vaccine-safety/topics/covid-19-vaccines/subcommittee, accessed 30 April 2026).

{25} Age cut-off should be determined by countries – often it is 75 or 80 years. 

{26}  Age cut-off should be determined by countries – often it is 50 or 60 years 

{27} WHO standardized definition for adults: Post-COVID-19 condition occurs in individuals with a history of probable or confirmed SARS-CoV-2 infection, usually 3 months from the onset of COVID-19, with symptoms that last for at least 2 months and cannot be explained by an alternative diagnosis. (https://www.who.int/publications/i/item/WHO-2019-nCoV-Post_COVID-19_condition-Clinical_case_definition-2021.1, accessed 30 April 2026);  WHO standardized definition for children and adolescents: Post-COVID-19 condition in children and adolescents occurs in individuals with a history of confirmed SARS-CoV-2 infection, with at least one persistent physical symptom lasting for at least 12 weeks after testing positive, that impacts everyday functioning and cannot be explained by another diagnosis. (https://www.who.int/publications/i/item/WHO-2019-nCoV-Post-COVID-19-condition-CA-Clinical-case-definition-2023-1, accessed 30 April 2026) 

{28} WHO SAGE Roadmap for prioritizing uses of COVID-19 vaccines (https://www.who.int/publications/i/item/WHO-2019-nCoV-Vaccines-SAGE-Prioritization-2023.1, accessed 30 April 2026)

(...)

Source: 

Link: https://www.who.int/publications/journals/weekly-epidemiological-record

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Experts convened by #WHO advise on candidate #treatments and #vaccines for #Ebola disease caused by #Bundibugyo virus (WHO, May 28 '26)

 

    In response to the current outbreak of Ebola disease caused by Bundibugyo virus occurring in the Democratic Republic of the Congo, with cases also reported in Uganda, WHO convened several of its expert and advisory groups. 

    These groups assessed potential vaccines and therapeutics for both prevention and treatment of Bundibugyo virus disease (BVD). 

    The WHO advisory groups recommended that all the products identified and considered be used exclusively within clinical trials to generate robust data and ensure safe, ethical, and effective research.

    WHO convened a series of meetings with the WHO R&D Blueprint technical advisory groups on candidate vaccines and therapeutics for BVD.

    In parallel, WHO also convened the Strategic Advisory Group of Experts on Immunization (SAGE) and its Ebola vaccine working group to advise on the potential role of licensed Ebola vaccines during BVD outbreaks.

Key recommendations

    There are currently no licensed therapeutics or vaccines specifically approved for the prevention and treatment of BVD. 

    Nevertheless, WHO advisory groups considered several candidate products that are promising enough to warrant prioritization for evaluation in clinical trials. 

    WHO is now working closely with the governments of the Democratic Republic of the Congo and Uganda to facilitate the implementation of research evaluation of these products.

    For treatment of cases:

        ° For treatment, the independent experts recommended prioritizing three candidate therapeutics for evaluation in research (i.e. clinical trials) among confirmed BVD cases: the monoclonal antibodies MBP134 and Maftivimab®, as well as the antiviral remdesivir.

        ° Combination therapy using a monoclonal antibody and remdesivir is also recommended for evaluation.

    For prevention of cases:

        ° For post-exposure prophylaxis among contacts of confirmed and probable cases, the oral antiviral obeldesivir was determined to be a priority candidate, although experts noted that this approach depends on effective contact tracing, which remains operationally challenging in some of the affected areas of the Democratic Republic of the Congo. Research on post-exposure prophylaxis involves giving tablets of obeldesivir to contacts of cases to evaluate whether this prevents them from developing Ebola disease.

        ° The most promising candidate vaccine was determined by the experts to be the single-dose rVSV Bundibugyo vaccine (being developed by the International AIDS Vaccine Initiative or IAVI). The development of this single-dose vaccine candidate will likely require 7–9 months before it is ready to be assessed through a clinical trial for its ability to prevent BDV.

        ° Another candidate vaccine, ChAdOx1 Bundibugyo (being developed by Oxford University/Serum Institute of India) could potentially become available within 2–3 months for efficacy assessment through a clinical trial.  However, additional animal data are still required to support and confirm further prioritization. Experts noted that a single-dose vaccine approach of this candidate could be suitable for contacts of Ebola cases, whereas a two-dose strategy might be considered for high-risk but unexposed populations such as health-care workers and frontline responders.

        ° The convened experts also reviewed the potential role of Ervebo, the only licensed Ebola vaccine. It is approved for use during outbreaks caused by the most common Ebola virus in Africa, from the Orthoebolavirus family. Ervebo is not licensed for prevention of BVD and evidence on cross-protection to other Ebola virus species remains limited and inconclusive. WHO recommends that Ervebo should not be used outside carefully designed research settings, to allow for its performance against BDV to be assessed.

Ensuring ethical and safe clinical trials

    WHO, the governments of the Democratic Republic of the Congo and Uganda, the Africa Centres for Disease Control and Prevention (Africa CDC), the ANRS Emerging infectious diseases (French National Agency for Research on AIDS and Viral Hepatitis), and other scientific partners are working together to develop and implement appropriate protocols to assess the safety and efficacy of the prioritized therapeutics through clinical field trials.

    WHO calls for accelerated access to essential supplies, stronger community protection, engagement and trust, and coordinated investment in the research, development and evaluation of BVD countermeasures.

    All research must adhere to the highest ethical standards, under the leadership of the national health authorities and in close consultation with affected communities.

    In the meantime, our priority is to stop transmission with tools that we have used for decades of Ebola responses, which include disease surveillance, rapid testing and diagnosis, contact tracing, isolation and care for patients, infection prevention and control, community engagement, and safe and dignified burials.

Background

    The WHO R&D Blueprint is a global initiative that allows the rapid activation of research and development activities during epidemics. Its aim is to fast-track the availability of proven effective tests, vaccines, and medicines that can be used to save lives and avert large-scale crises.

    SAGE is the principal advisory group to WHO for vaccines and immunization. It is charged with advising WHO on overall global policies and strategies, ranging from vaccines and technology, research and development, to delivery of immunization and its linkages with other health interventions.

About WHO 

    Dedicated to the well-being of all people and guided by science, the World Health Organization leads and champions global efforts to give everyone, everywhere an equal chance at a safe and healthy life.

    We are the UN agency for health that connects nations, partners and people on the front lines in 150+ locations – leading the world’s response to health emergencies, preventing disease, addressing the root causes of health issues and expanding access to medicines and health care. Our mission is to promote health, keep the world safe and serve the vulnerable. 

    “Together for health. Stand with science”, the theme of World Health Day 2026 marks a year-long campaign to highlight science as the foundation for protecting health and well-being worldwide.

Source: 

Link: https://www.who.int/news/item/28-05-2026-experts-convened-by-who-advise-on-candidate-treatments-and-vaccines-for-ebola-disease-caused-by-bundibugyo-virus

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BNT162b2 #LP81 early #vaccine #effectiveness against #COVID19 emergency department, urgent care, and outpatient visits

 

Abstract

COVID-19 continues to cause substantial illness, particularly among older adults and individuals with underlying conditions. Updated vaccines are designed to better protect against the strains of the virus that are currently circulating. However, real-world evidence on the effectiveness of updated vaccines remains limited. Here we show the early vaccine effectiveness (VE) of the BNT162b2 LP.8.1-adapted COVID-19 vaccine against mild-to-moderate COVID-19 outcomes. We used a test-negative case-control design to estimate early VE of the BNT162b2 LP.8.1-adapted vaccine against COVID-19 emergency department/urgent care (ED/UC) and outpatient visits. Adult patients from the US Veterans Affairs Healthcare System with an acute respiratory infection (ARI) who underwent SARS-CoV-2 testing from September 10 to November 30, 2025, were included. VE was estimated using multivariable logistic regression adjusted for patient demographics and clinical characteristics. Among 34,455 ARI episodes, 10.7% were COVID-19 cases. A total of 1.2% of cases and 2.6% of controls received the BNT162b2 LP.8.1 vaccine, with a median time since vaccination of 29 days (interquartile range 20-–41). BNT162b2 LP.8.1 vaccine was effective during the early 2025–2026 respiratory virus season. VE was 57% (95% confidence interval [CI] 39–70%) against ED/UC visits and 54% (95% CI 15–75%) against outpatient visits. These findings inform shared decision-making in clinical practice and support the continued importance of COVID-19 vaccination in populations for whom it is recommended.

Source: 

Link: https://www.nature.com/articles/s41467-026-73798-3

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Understanding the emergence of the #influenza #H3N2 K #subclade in its historical and evolutionary context

Abstract

The emergence in 2025/26 of the influenza A/H3N2 K substrain (H3N2/K) was the cause of significant public health concern. This genetically divergent virus was assessed to have a strongly decreased reactivity to contemporary vaccine strains. Respectively prolonged and early influenza seasons in the Southern and Northern Hemispheres contributed to concerns about vaccine efficacy. Here we retrospectively assessed the genetic and antigenic properties of this virus, combining epidemiological surveillance data, computational antigenic analysis, and serological data using samples from a well-stratified UK cohort. In contrast to initial indications, we found that despite the genetic distinctiveness of H3N2/K the virus had undergone limited antigenic change, suggesting that its emergence was instead the result of selection for non-antigenic properties. We confirmed previous results showing that contemporary vaccines produced an enhanced neutralising response to H3N2/K but, in a stratified serological analysis, showed that responses to the J and K substrains were age-dependent, largely driven by patterns of vaccination. Our results have implications for antigenic surveillance and for public communication strategies in future influenza seasons.

Competing Interest Statement

PRM declares funding by MSD. EH has received an honorarium for advisory board work for Seqirus.

Funder Information Declared

Medical Research Council, MR/Y03368X/1, MC_UU_0034/1, MC_UU_0034/2, MC_UU_0034/3, MC_UU_0034/5, MC_UU_0034/6

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.21.726823v1

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Molecular Characterization of #H5N1 Clade 2.3.4.4B Virus in Vaccinated Layer #Chickens

 

Abstract

The global emergence of the avian influenza virus (AIV) H5N1 clade 2.3.4.4B since 2016 has caused substantial losses in wild bird and poultry populations, along with heightened risks of transmission to humans and other mammals. Vaccination of poultry has been a key strategy to curb the virus’s spread and mitigate its socioeconomic impact. This report describes an outbreak of high pathogenicity avian influenza virus (HPAIV) H5N1 clade 2.3.4.4B in a flock of 15,000 brown layer chickens (170 days old), all of which had received a four-dose vaccination regimen with H5N1/H5N8 commercial vaccines at 17, 50, 100, and 125 days of age. Despite this vaccination history, H5N1 infection was confirmed approximately seven weeks post-vaccination. H5N1 infection was confirmed by RT-qPCR, virus isolation, and full genome sequencing covering all eight gene segments, followed by phylogenetic and molecular analyses. Clinical signs included reduced feed intake, decreased egg production, and a cumulative mortality rate of 35% over 52 days. Hemagglutination inhibition (HI) testing with various H5 antigens revealed inconsistent antibody titers (geometric mean: 4.0 to 9.1 log2). Genetic analysis of the full-length HA and NA gene sequences further revealed strong similarity to contemporaneous H5N1 clade 2.3.4.4B strains circulating in Egypt, with multiple mutations in the HA head domain, particularly near immunogenic epitopes and receptor binding sites. These findings highlight the limitations of current vaccination strategies under conditions of antigenic mismatch and complex immunization schedules, emphasizing the need for improved vaccine matching and continuous molecular surveillance. To improve outbreak management in poultry, enhanced vaccination protocols, stringent biosecurity measures, and rigorous monitoring practices are critical.

Source: 

Link: https://www.mdpi.com/1999-4915/18/6/589

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#Statement on the #antigen #composition of #COVID19 #vaccines (#WHO, May 16 '26)

 

Key points:

    -- The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) held its twice-yearly decision-making meeting in May 2026 to review the evolution of SARS-CoV-2, the effectiveness of currently approved COVID-19 vaccines and the implications for COVID-19 vaccine antigen composition.

    -- The objective of any update to COVID-19 vaccine antigen composition is to enhance vaccine-induced immune responses to circulating SARS-CoV-2 variants, when needed.

    -- Following this meeting, the TAG-CO-VAC advises vaccine manufacturers that monovalent LP.8.1 is the recommended vaccine antigen.

    -- Other antigens (e.g. XFG, NB.1.8.1) or other approaches that demonstrate broad and robust neutralizing antibody responses or efficacy against currently circulating SARS-CoV-2 variants could also be used.

    -- Vaccination remains an important public health countermeasure against COVID-19 and vaccination should not be delayed in anticipation of access to vaccines with an updated antigen composition. As per the March 2026 WHO Strategic Advisory Group of Experts on Immunization (SAGE) recommendations, Member States should consider routine COVID-19 vaccination of groups at highest risk of severe COVID-19 disease.

    -- The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to closely monitor the genetic and antigenic evolution of SARS-CoV-2 variants, immune responses to SARS-CoV-2 infection and COVID-19 vaccination, and the effectiveness of COVID-19 vaccines against circulating variants. 

    -- Based on these evaluations, WHO advises vaccine manufacturers and regulatory authorities on the implications for future updates to COVID-19 vaccine antigen composition. 

    -- In December 2025, the TAG-CO-VAC advised vaccine manufacturers that monovalent LP.8.1 is the recommended vaccine antigen. Multiple manufacturers (using mRNA or recombinant protein-based vaccines) have updated COVID-19 vaccine antigen composition to monovalent LP.8.1 formulation. Several of these vaccines have been approved for use by regulatory authorities and have been introduced into vaccination programmes. Previous statements from the TAG-CO-VAC can be found on the WHO website.

    -- The TAG-CO-VAC reconvened on 7-8 May 2026 to review the genetic and antigenic evolution of SARS-CoV-2; immune responses to SARS-CoV-2 infection and/or COVID-19 vaccination; the effectiveness of currently approved vaccines against circulating SARS-CoV-2 variants; and the implications for COVID-19 vaccine antigen composition.

Evidence reviewed

    -- The published and unpublished evidence reviewed by the TAG-CO-VAC included: 

    (1) SARS-CoV-2 genetic evolution, with additional support from the WHO Technical Advisory Group on Virus Evolution (TAG-VE); 

    (2) Antigenic characterization of previous and emerging SARS-CoV-2 variants using virus neutralization tests with animal antisera and further analysis of antigenic relationships using antigenic cartography; 

    (3) Immunogenicity data on the breadth of neutralizing antibody responses elicited by currently approved vaccine antigens against circulating SARS-CoV-2 variants using animal and human sera, with additional support from WHO Coronavirus Network (CoViNet); 

    (4) Preliminary clinical immunogenicity data on immune responses following infection with circulating SARS-CoV-2 variants; 

    (5) Available COVID-19 vaccine effectiveness (VE) estimates of currently approved vaccines; and 

    (6) Preliminary non-clinical and clinical immunogenicity data on the performance of candidate vaccines with updated antigens shared by vaccine manufacturers with TAG-CO-VAC. 

    Further details on the data reviewed by the TAG-CO-VAC can be found in the accompanying data annex. Confidential data reviewed by the TAG-CO-VAC are not shown.

Summary of available evidence

    There are persistent and increasing gaps and delays in the surveillance and reporting of cases, hospitalizations and deaths from WHO Member States, limiting the interpretation and comparability of epidemiological trends over time. 

    In 2026, SARS-CoV-2 continues to circulate globally, causing severe disease, post COVID-19 condition, and death. 

    However, the impact on health systems has reduced substantially compared to 2020-2021 due to multiple factors, including increased population immunity from infection and/or vaccination and improved clinical management. 

    In 2026, all WHO regions are reporting lower SARS-CoV-2 test positivity rates than during the corresponding period in previous years.

    Globally, the current predominant variant among SARS-CoV-2 sequences remains Variant Under Monitoring (VUM) XFG, however the weekly proportion is now declining. 

    In contrast, in countries in the WHO Western Pacific Region where sequencing continues, VUM NB.1.8.1 is the predominant variant. 

    Globally, the proportion of VUM BA.3.2 is increasing, with heterogeneous dynamics across countries where genomic surveillance continues. 

    BA.3.2 appears to have lower fitness than JN.1-descendant variants, which may explain why BA.3.2 has not displaced JN.1-descendant variants in regions where it has been detected. 

    To date, the increase in the proportion of BA.3.2 does not appear to be associated with a substantial increase in disease burden, unlike increases associated with previous Variants of Interest and JN.1-descendant variants. 

    In several countries, BA.3.2 appears to account for a higher proportion of sequences from young children than adults, suggesting possible differences in susceptibility to BA.3.2 related to a lack of cross-reactive immunity generated by previous exposure to early SARS-CoV-2 variants. 

    However, sequence numbers and the reported number of infected individuals, including those with severe disease, remain low; this observation should therefore be interpreted with caution.

    Neutralization data using antisera from naïve animals infected or vaccinated with JN.1, LP.8.1, NB.1.8.1 or XFG, indicated that recent JN.1-descendant variants are antigenically closely related. 

    These variants differed by approximately 1 antigenic unit in cartographic analyses, corresponding to a two-fold-difference in neutralization, with XFG often the most antigenically distant from JN.1 within the JN.1 cluster. 

    In contrast, these antisera showed limited neutralizing activity against BA.3.2. 

    Antisera from naïve animals infected with BA.3.2 showed very limited cross-reactivity with recent JN.1-descendant variants. 

    Together, these results indicate that BA.3.2 is antigenically distinct from JN.1- descendant variants.

    Sera from cohorts that are representative of recent population immunity and pre-LP.8.1 vaccination sera demonstrated cross-reactivity with recent JN.1-descendant variants and with BA.3.2.

    Pre- and post-vaccination sera from individuals immunized with LP.8.1 demonstrated significant increases in neutralizing activity against JN.1 and its descendant variants, including NB.1.8.1 and XFG. 

    Post-vaccination neutralizing antibody titers and the fold change against BA.3.2 were lower than against the homologous LP.8.1 antigen and other JN.1- descendant variants.

    Pre- and post-vaccination sera from individuals immunized with JN.1 or KP.2 demonstrated significant increases in neutralizing activity against JN.1 and its descendant variants. 

    However, post-vaccination neutralizing antibody titers against NB.1.8.1 and XFG were lower than those against the homologous JN.1 or KP.2 antigens, with even larger reductions typically observed for BA.3.2.

    Contemporary vaccine effectiveness (VE) estimates are relative (rVE) and demonstrate the added or incremental protection of recent vaccination over and above pre-existing infection- and vaccine-derived immunity. 

    Monovalent JN.1 and KP.2 mRNA vaccines demonstrated additional protection—relative to pre-existing immunity—against symptomatic and severe COVID-19. 

    The limited number of rVE estimates using monovalent LP.8.1 vaccines also demonstrated additional protection against symptomatic and severe COVID-19.

    Data shared with the TAG-CO-VAC by vaccine manufacturers showed that:

      - Immunization of naïve mice with monovalent LP.8.1, XFG or NB.1.8.1 induced high neutralizing antibody titers against the homologous antigen, as well as other JN.1-descendant variants. 

    - Low or non-detectable neutralizing antibody titers were consistently observed against BA.3.2. 

    - In contrast, immunization of naïve mice with monovalent BA.3.2 induced immune responses largely restricted to the homologous antigen. 

    - Overall immunogenicity of BA.3.2 was lower than after LP.8.1, XFG or NB.1.8.1 immunization.

    - Immunization of mice previously immunized with SARS-CoV-2 variants and then immunized with LP.8.1, XFG or NB.1.8.1 induced high neutralizing antibody titers against JN.1-descendant variants. 

    - Lower neutralizing antibody titers against BA.3.2 were observed. 

    - Immunization with BA.3.2 induced neutralizing titers against the homologous antigen, and to a lesser extent against JN.1-descedant variants. 

    - However, overall immunogenicity of BA.3.2 was lower than after LP.8.1, XFG or NB.1.8.1 immunization.

    - In humans, vaccination with 8.1 induced strong increases in neutralizing antibody titers against JN.1, LP.8.1, NB.1.8.1 and XFG. 

    - As in mice, post- vaccination neutralizing antibody titers against BA.3.2 were lower than those against the homologous LP.8.1 antigen. 

    - A single clinical immunogenicity study using a BA.3.2 vaccine candidate showed increased neutralizing antibody titers against the homologous antigen, and a back boost against JN.1-descendant variants, but overall lower immunogenicity than the LP.8.1 vaccine.

    - Overall, LP.8.1 as a vaccine antigen in populations with high levels of prior infection and / or vaccination continues to induce broadly cross-reactive immune responses to circulating SARS-CoV-2 variants.

    -- The TAG-CO-VAC acknowledges several limitations of available data:

    - There are persistent and increasing gaps and delays in the reporting of cases, hospitalizations and deaths, from WHO Member States, as well as in genetic/genomic surveillance of SARS-CoV-2 globally, including low numbers of samples sequenced and limited geographic diversity. The TAG-CO-VAC strongly supports the ongoing work of the WHO Coronavirus Network (CoViNet) and the Global Influenza Surveillance and Response System (GISRS) to address this information gap.

    - The timing, specific mutations and antigenic characteristics of emerging and future variants are difficult to predict, and the potential public health impact of these variants remain unknown. Currently, two antigenically distinct lineages (JN.1-descendant and BA.3.2-descendant variants) are circulating and the comparative evolutionary potential of these lineages remains uncertain. Variants derived from these lineages will continue to be monitored and/or characterized, and the TAG-CO-VAC strongly supports the ongoing work of the TAG-VE. 

    - Although neutralizing antibody titers have been shown to be important correlates of protection from SARS-CoV-2 infection and of estimates of vaccine effectiveness, there are multiple components of immune protection elicited by infection and/or vaccination. Data on the immune responses following JN.1-descendant variant infection or monovalent LP.8.1 vaccination are largely restricted to neutralizing antibodies. Data and interpretation of other aspects of the immune response, including cellular immunity, are limited. 

    - Immunogenicity data against currently circulating SARS-CoV-2 variants are not available for all COVID-19 vaccines. 

    - Recent estimates of rVE are limited in terms of the number of studies, geographic diversity, vaccine platforms evaluated, populations assessed, duration of follow-up, and contemporary comparisons of vaccines with different antigen composition. There are currently only a limited number of available rVE estimates using monovalent LP.8.1 mRNA vaccines; there are no rVE estimates in populations in which BA.3.2 was the predominant variant.

Recommendations for COVID-19 vaccine antigen composition

    -- Monovalent LP.8.1 (Nextstrain: 25A; GenBank: PV074550.1; GISAID: EPI_ISL_19467828) is the recommended COVID-19 vaccine antigen.

    -- Other antigens (e.g. XFG, NB.1.8.1) or other approaches that demonstrate broad and robust neutralizing antibody responses or efficacy against currently circulating SARS-CoV-2 variants could also be used.

    -- As per the March 2026 WHO Strategic Advisory Group of Experts on Immunization (SAGE) recommendations, Member States should consider routine COVID-19 vaccination of groups at highest risk of severe COVID-19 disease and vaccination should not be delayed in anticipation of access to vaccines with an updated antigen composition.

Further data requested

    -- Given the limitations of the evidence upon which the recommendations above are derived and the anticipated continued evolution of the virus, the TAG-CO-VAC strongly encourages generation of the following data (in addition to the types of data outlined in March 2026)

    - Immune responses and clinical endpoints (i.e. VE and/or comparator rates of infection and severe disease) in varied human populations who receive currently approved COVID-19 vaccines against emerging SARS-CoV-2 variants, across different vaccine platforms.

    - Strengthened epidemiological and virological surveillance, as per the Standing Recommendations for COVID-19 in accordance with the International Health Regulations (2005), to determine if emerging variants are antigenically distinct and able to displace circulating variants.

    - Strengthened epidemiological surveillance to characterize disease severity in immunologically naïve and/ or immature individuals (e.g. young pediatric cohorts), particularly for BA.3.2 infections.

    - Non-clinical and clinical immunogenicity data against circulating SARS-CoV-2 variants for vaccine candidates with different SARS-CoV-2 antigens.

    - As previously stated, the TAG-CO-VAC continues to encourage the further development of vaccines that may improve protection against infection and reduce transmission of SARS-CoV-2.

    -- The TAG-CO-VAC will continue to closely monitor the genetic and antigenic evolution of SARS-CoV-2 variants, immune responses to SARS-CoV-2 infection and COVID-19 vaccination, and the effectiveness of COVID-19 vaccines against circulating variants. The TAG-CO-VAC will also continue to reconvene every six months, or as needed, to evaluate the implications for COVID-19 vaccine antigen composition. At each meeting, recommendations to either maintain current vaccine composition or to consider updates will be issued. Prior to each meeting, the TAG-CO-VAC will publish an update to the statement on the types of data requested to inform COVID-19 vaccine antigen composition deliberations.

Source: 

Link: https://www.who.int/news/item/16-05-2026-statement-on-the-antigen-composition-of-covid-19-vaccines

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Membrane-anchored #influenza #neuraminidase vaccine drives #human-like broadly protective B cell responses

 

Abstract

Influenza neuraminidase (NA) is a promising target for universal flu vaccines, yet eliciting potent B-cell responses against its conserved epitopes remains challenging. Here, we developed a membrane-anchored, folding-domain-free NA (mNA) that elicited superior head-specific germinal center B cell and antibody responses compared to soluble tetrameric NA. In non-human primates, mNA immunization induced cross-reactive memory B cell (MBC) responses, expanding clones with the conserved DR motif in HCDR3, a hallmark of human broadly reactive NA antibodies. These MBCs conferred cross-inhibitory activity against diverse NA variants and in vivo cross-protection. Cryo-EM analysis revealed that the 554-C2 clone targets the conserved enzymatic pocket via the DR motif, while the 554-C1 clone recognizes previously uncharacterized epitopes at the interface between two adjacent N2 monomers, effectively reducing plaque formation by contemporary H3N2 strains. Our findings highlight the immunological advantages of membrane-anchoring, providing a robust strategy for designing next-generation vaccines against influenza and other pathogens.

Competing Interest Statement

Westlake University has filed for patent protection for mNA used as an influenza vaccine.

Funder Information Declared

State Key Laboratory of Gene Expression, SKLGE-ZX-2025007

Zhejiang Provincial Key Laboratory Construction Project, 2024ZY01026, 2024E10060, 2024E10052

Natural Science Foundation of Zhejiang province, LR26H190001

National Natural Science Foundation of China, 82471855, 825B2062, 82330054, 82502209, 32471303

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.13.724804v1

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The Decline in #Influenza #Antibody Titers and Modifiers of #Vaccine #Immunity from over Ten Years of Serological Data

 

Abstract

Annual influenza vaccination is the cornerstone for seasonal protection, yet antibody responses are highly variable across individuals and over time. To systematically assess the determinants of this heterogeneity, we compiled 20,449 hemagglutination inhibition and neutralization titers from 4,540 participants enrolled in 14 new vaccine studies we conducted and 50 prior studies that collectively span 2010-2023. Seasonal effects dominated, with pre- and post-vaccination titers declining steadily from 2017 onwards, outweighing the influence of age, sex, or repeated vaccination. Titers to B Yamagata remained steady throughout all years examined, suggesting unique durability and offering a reason for lineage extinction. Vaccine timing emerged as a strong and previously underappreciated determinant of immunity, with individuals vaccinated later in the season exhibiting larger post-vaccination titers. Not being vaccinated or receiving the live-attenuated FluMist vaccine in one year significantly enhanced the response to inactivated vaccines in 45% or 68% of cohorts, respectively, whereas antigen dose and adjuvants had modest impact. These findings identify vaccine timing and seasonal context as underrecognized drivers of immunogenicity and provide actionable insights for optimizing influenza vaccination strategies.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

This research was supported by the the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH) under the Computational Models of Influenza Immunity (U01 AI187062), LJI & Kyowa Kirin, Inc. (KKNA - Kyowa Kirin North America), and the Bodman family (TE).

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.01.07.25342310v2

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Efficacy and #Safety of an #mRNA Seasonal #Influenza #Vaccine in Adults

 

Abstract

Background

Seasonal influenza causes substantial illness and death in adults 50 years of age or older, even with current vaccines. An investigational messenger RNA (mRNA)–based vaccine called mRNA-1010 encodes hemagglutinin glycoproteins from World Health Organization–recommended influenza strains.

Methods

In this phase 3, double-blind, active-controlled trial, we randomly assigned adults 50 years of age or older to receive trivalent mRNA-1010 (37.5 μg, which includes 12.5 μg of each strain) or a licensed standard-dose comparator. The primary efficacy end point was relative vaccine efficacy against reverse-transcriptase–polymerase-chain-reaction (RT-PCR)–confirmed, protocol-defined influenza-like illness caused by influenza A or B, from at least 14 days after vaccination through the end of the influenza season. Hypothesis testing was conducted hierarchically to assess noninferiority (lower boundary of the 95% confidence interval [CI], >−10%), superiority (lower boundary of the 95% CI, >0%), and a higher level of superiority (lower boundary of the 95% CI, >9.1%).

Results

A total of 40,703 participants received mRNA-1010 (20,350 participants) or the standard-dose comparator (20,353 participants); the median follow-up was 181 days (range, 1 to 227). RT-PCR–confirmed, protocol-defined influenza-like illness was observed in 411 of 20,179 recipients of mRNA-1010 (2.0%) and 557 of 20,124 recipients of the standard-dose comparator (2.8%), which corresponds to a relative vaccine efficacy of 26.6% (95% CI, 16.7 to 35.4), thereby meeting the criteria for noninferiority, superiority, and higher-level superiority. Solicited adverse reactions were more frequent with mRNA-1010 than with the standard-dose comparator (injection-site pain in 65.8% vs. 29.8%, fatigue in 45.1% vs. 20.3%, headache in 37.8% vs. 18.0%, and myalgia in 35.4% vs. 11.6%); most reactions were mild to moderate and transient. Serious adverse events were reported in 2.2% of the recipients of mRNA-1010 (with three events considered by the investigator to be vaccine-related) and in 1.9% of the recipients of the standard-dose comparator (with two events considered by the investigator to be vaccine-related).

Conclusions

In this trial, mRNA-1010 was superior to standard-dose licensed vaccines for prevention of RT-PCR–confirmed, protocol-defined influenza-like illness in adults 50 years of age or older. Solicited adverse reactions were more frequent with mRNA-1010. (Funded by Blackstone Life Sciences and Moderna; Fluent ClinicalTrials.gov number, NCT06602024.)

Source: 

Link: https://www.nejm.org/doi/full/10.1056/NEJMoa2516491?query=TOC

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Evaluation of Cross-Immunogenicity of #Ferret #Antisera Following Immunization with #H5N1 #Vaccine Strains

 

Abstract

Background: 

Highly pathogenic avian influenza H5N1 viruses of clade 2.3.4.4b have spread globally since 2021, causing extensive outbreaks in avian populations and repeated spillovers into diverse mammalian hosts, including humans. These cross-species transmission events highlight ongoing pandemic risks and underscore the need for vaccine strategies that reflect viral evolution at the human–animal interface. Despite the availability of licensed H5 vaccines and newly recommended World Health Organization (WHO) candidate vaccine viruses (CVVs), the extent to which these vaccines elicit cross-reactive antibody responses against contemporary clade 2.3.4.4b viruses, including mammalian spillover isolates of avian origin, remains incompletely characterized. 

Method: 

In this study, ferret antisera were generated using four WHO-recommended H5 CVVs, including a clade 1 strain (A/Vietnam/1194/2004) and three clade 2.3.4.4b strains (A/Astrakhan/3212/2020, A/American wigeon/South Carolina/22-000345-001/2021, and A/Ezo red fox/Hokkaido/1/2022), formulated with alum adjuvant to reflect licensed vaccine formulation used in national preparedness programs. Antibody responses and cross-reactive activity were evaluated using hemagglutination inhibition (HI) and microneutralization (MN) assays against homologous vaccine strains and a feline-origin clade 2.3.4.4b H5N1 field isolate from Korea, A/Feline/Korea/SNU-01/2023. 

Results: 

Antisera induced by clade 2.3.4.4b CVVs showed cross-reactive antibody responses against homologous and heterologous clade 2.3.4.4b viruses and demonstrated measurable HI and MN responses against the feline-origin field isolate. In contrast, antisera raised against the clade 1 Vietnam CVV exhibited limited cross-reactivity against clade 2.3.4.4b viruses. Overall, clade 2.3.4.4b CVVs generally showed higher antibody responses than the clade 1 vaccine strain across multiple panels. 

Conclusions: 

These findings provide descriptive insights into antigenic differences between clade 1 and clade 2.3.4.4b viruses and support the antigenic relevance of clade 2.3.4.4b CVVs for contemporary H5N1 strains. This study highlights the importance of ongoing antigenic evaluation to inform vaccine strain selection within a One Health framework.

Source: 

Link: https://www.mdpi.com/2076-393X/14/4/301

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A Phase 1/2 Dose-Ranging Safety and Immunogenicity Study of #mRNA-Based Candidate #Pandemic #Influenza #Vaccines in Healthy Adults

 

Abstract

Background

Influenza A viruses pose a persistent pandemic threat. We report safety, reactogenicity, and immunogenicity findings for mRNA-1018 pandemic influenza vaccine candidates from a phase 1/2 study in healthy adults.

Methods

In Part A, participants were randomized to receive 1 of 4 mRNA-1018 candidates at 1 of 3 dose levels across 2 influenza A groups: (1) H5N8/H5-only or (2) H7N9/H7-only. H5N8 and H7N9 candidates were administered at 25, 50, or 100-µg and H5-only and H7-only at 12.5, 25, or 50-µg. Part B participants were randomized to receive 12.5, 25, or 50-µg H5-only-CG. Primary objectives were to evaluate the safety and reactogenicity of vaccine candidates. Secondary objectives included evaluation of humoral immunogenicity through day 205 by hemagglutination inhibition (HAI), neuraminidase inhibition, and microneutralization assays.

Results

Parts A and B comprised 1195 and 304 dosed participants, respectively. Overall, solicited local adverse reactions (ARs) within 7 days of vaccination occurred in 76.8% of participants across vaccine candidates and dose levels, most commonly injection-site pain. Solicited systemic ARs were reported in 62.8% of participants, most frequently fatigue and headache. Solicited ARs were predominantly grade 1–2 in severity, with few grade 3 and no grade 4 events. Post-vaccination immune responses, assessed absolutely, by HAI titers and dynamically, by seroconversion rates, tended to increase with vaccine dose. H5-based candidates induced stronger strain-specific HAI, but with comparable microneutralization titers, versus H7-based candidates.

Conclusions

Vaccine candidates were sufficiently well-tolerated and immunogenic. Further development of mRNA pandemic influenza vaccines is warranted for pandemic preparedness.

Source: 

Link: https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciag278/8662346

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#Prion shedding is reduced by chronic wasting disease {#CWD} #vaccination

 

Abstract

Chronic wasting disease (CWD) is a strictly fatal and highly contagious prion disease of wild and farmed cervids currently expanding in North America. Prion diseases are caused by conversion of the cellular prion protein to its pathological isoform PrPSc. Vaccination is considered a promising strategy to contain CWD, even though prion diseases do not show classical immune responses. For CWD containment, it is important that vaccines reduce shedding of prions in excreta, a major contributor to transmission. Here, we tested the effect of vaccines on prion shedding in feces and urine by vaccinating and prion infecting knock-in mice that recapitulate CWD pathogenesis as found in cervids. Vaccination reduced or even prevented CWD shedding in feces and urine collected between 30–90% of incubation time to disease. This is the first report showing that prion shedding can be blocked in a prion disease. For CWD specifically it may reduce the environmental prion burden and break the disease transmission cycle.

Source: 

Link: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014166

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#Measles - #Bangladesh (WHO, D.O.N., April 23 '26)

 

Situation at a glance

On 4 April 2026, the National International Health Regulations (IHR) Focal Point for Bangladesh notified WHO of a nationwide increase in measles cases, geographically affecting 58 out of 64 districts across all eight divisions in Bangladesh. 

A total of 19 161 suspected measles cases and 2897 laboratory-confirmed measles cases have been reported between 15 March and 14 April 2026, including 166 measles related deaths (CFR 0.9%). 

The majority (79%) of the reported cases are children aged under 5 years. 

A targeted measles-rubella (MR) vaccination campaign started on 5 April, and various outbreak response measures are ongoing including strengthening nationwide surveillance and epidemiological analysis to enhance case detection and reporting. 

Based on currently available information, WHO assesses the risk at the national level as high due to ongoing transmission across multiple divisions, the large number of susceptible children, documented immunity gaps, and the occurrence of suspected measles-related deaths.

Description of the situation

On 4 April 2026, the National IHR Focal Point of Bangladesh notified WHO of a significant increase in measles cases, driven by sustained domestic transmission. 

Since January 2026, Bangladesh has experienced a marked increase in measles cases. 

Geographically, cases have been reported across all eight divisions, in 58 out of 64 districts (91% of districts), indicating widespread transmission nationally.  

Since 15 March 2026 and as of 14 April, a total of 19 161 suspected measles cases and 2973 laboratory-confirmed measles cases have been reported. 

Moreover, 166 suspected measles-related deaths (CFR 0.9%) and 30 confirmed measles-related deaths (CFR= 1.1%) have been recorded. 

A total of 12 318 hospital admissions and 9772 hospital discharges have also been reported. 

The highest cumulative burden of suspected measles cases since 15 March 2026 has been reported in Dhaka (8263 cases), Rajshahi (3747 cases), Chattogram (2514 cases), and Khulna (1568 cases). 

In Dhaka, cases are concentrated in densely populated informal settlements, including Demra, Jatrabari, Kamrangirchar, Korail, Mirpur, and Tejgaon industrial and slum clusters.  (HEOC, DGHS, 15 April 2026).

Children aged under 5 years account for the majority of reported cases (79%), including children aged under 2 years (66%) and infants aged under 9 months (33%). 

A total of 166 suspected deaths have been reported (CFR 1%), mainly among unvaccinated children aged under 2 years.

Epidemiology

Measles is a highly contagious acute viral disease which affects individuals of all ages and remains one of the leading causes of death among young children globally. The mode of transmission is airborne or via droplets from the nose, mouth, or throat of infected persons.

Initial symptoms, which usually appear 10-14 days (range 7-23 days) after infection, include high fever, usually accompanied by a runny nose, bloodshot eyes, cough and tiny white spots inside the mouth. The rash usually appears 10-14 days after exposure and spreads from the head to the trunk to the lower extremities. A person is infectious from four days before up to four days after the appearance of the rash. There is no specific antiviral treatment for measles, and most people recover within 2-3 weeks.

Measles is usually a mild or moderately severe disease. However, measles can lead to complications such as pneumonia, diarrhoea, secondary ear infection, inflammation of the brain (encephalitis), blindness, and death. Postinfectious encephalitis can occur in about one in every 1000 reported cases. About two or three deaths may occur for every 1000 reported cases.

Vaccination with measles containing vaccine is safe and effective, providing protection against measles and its complications for all eligible populations. WHO recommends two doses of Measles Containing Vaccine (MCV) to be provided through the routine immunization schedule. Strong routine immunization systems are therefore critical foundations for achieving and sustaining high levels of population immunity to vaccine preventable diseases such as measles.

WHO further recommends the conduct of Supplementary Immunization Activities (SIAs) or mass immunization campaigns as an effective strategy for delivering vaccination to children who may have been missed by routine services. In protecting vulnerable populations against measles, mass vaccination campaigns can rapidly improve population immunity by reducing the number of susceptible individuals in the population.

Public health response

A nationwide measles-rubella (MR) vaccination campaign was approved by the National Immunization Technical Advisory Group (NITAG) on 30 March 2026, targeting children aged 6–59 months (with expanded coverage for 6–8 months), and started on 5 April in 30 upazilas (sub-districts) of 18 priority districts. A nationwide campaign commenced on 20 April. 

Vitamin A campaign was held throughout the country on 15 March 2025.  During this outbreak response, Vitamin A supplementation is provided to all suspected and confirmed measles cases as an essential component of standard treatment and case management. 

District Rapid Response Teams (RRTs) have been activated, and vaccine procurement fast-tracked by the Ministry of Health. Other outbreak response actions include strengthening routine immunization to prevent further spread of the outbreak, enhancing hospital preparedness, ensuring availability of vitamin A, strengthening isolation capacity, and reinforcing infection prevention and control measures. 

Strengthening nationwide surveillance and epidemiological analysis, is also ongoing including measures to improve case detection and reporting. Trainings are being conducted at health facilities to improve case detection and reporting, and weekly situation reports produced to support evidence-based decision-making. 

National and divisional guidelines have been issued to guide response activities, including vaccination, clinical management, infection prevention and control, patient care pathways, and procurement. 

WHO risk assessment

Measles is a highly contagious viral disease that affects susceptible individuals of all ages and remains one of the leading causes of death among young children globally. Measles can cause serious illness in at-risk groups, including children under 5 years of age, those who are malnourished especially those with vitamin A deficiency and people with weakened immune systems. Measles complications include hearing loss, diarrhoea, pneumonia and blindness. Severe complications of measles include encephalitis, brain damage, and death. 

The current outbreak in Bangladesh is occurring in the context of suboptimal population immunity. A substantial proportion of cases occurred among children who were either unvaccinated or had received only one dose of measles-containing vaccine. In addition, some children were infected before reaching the age of eligibility for vaccination at 9 months. Most cases (91%) occurred among children aged 1 to 14 years, indicating substantial immunity gaps in this age group. 

Before this outbreak, Bangladesh had made substantial progress towards measles elimination. Reported coverage with the first dose of measles-containing vaccine increased considerably between 2000 (89% - WUENIC) and 2016 (118% - WUENIC), while coverage with the second dose also improved between its nationwide introduction in 2012 (22% - WUENIC) and 2024 (121% - WUENIC). During the same period, confirmed measles incidence declined sharply. However, recent declines in MR1 and MR2 coverage due to nationwide stockout of MR vaccine between 2024-2025, combined with routine immunization gaps and the absence of regular nationwide supplementary measles-rubella campaigns since 2020, have increased the number of susceptible children and contributed to the current outbreak. 

The risk at the national level is assessed as high due to ongoing transmission across multiple divisions, the large number of susceptible children, documented immunity gaps, and the occurrence of suspected measles-related deaths. The concentration of cases among unvaccinated and under-vaccinated children including infants too young to be vaccinated, raises concern for continued uninterrupted transmission and severe disease outcomes. 

Overall, the outbreak suggests a reversal from Bangladesh’s previous progress towards measles elimination and highlights increasing vulnerability to sustained transmission. Continued spread is likely unless urgent measures are implemented to strengthen surveillance, rapidly detect and respond to cases, and close immunity gaps through high-quality vaccination activities. 

There are considerable risks of cross-border spread, facilitated by cross-border population movement, with major urban centres such as Dhaka, Chattogram, Sylhet, and Cox’s Bazar being important international travel and transit hubs increasing the likelihood of national and international spread, particularly among unvaccinated or inadequately vaccinated travelers. 

Measles is endemic across the South-East Asia region. The risk is assessed as high at regional level.

Bangladesh shares extensive land borders with India and Myanmar, and population mobility across these borders may facilitate continued transmission. In Myanmar there is a considerable number of unvaccinated/zero dose children. With ongoing conflict and humanitarian crisis, surveillance and response capacities are limited. India, despite achieving high vaccination coverage, has reported a rise in case count over the past six months. Cities with high incidence such as Jashore and Chapainawabganj (an identified hotspot) share busy land crossings with India, thereby increasing the risk of introduction across the border. Despite Bangladesh’s progress towards measles elimination the current outbreak highlights the vulnerability of the population and underscores the fragility of immunization gains.

The risk at the global level is assessed as moderate due to high levels of population mobility, combined with ongoing widespread measles transmission and immunity gaps.

WHO advice

WHO recommends maintaining sustained homogeneous coverage of at least 95% with the first and second doses of the MCV vaccine in all municipalities and strengthening integrated epidemiological surveillance of measles and rubella to achieve timely detection of all suspected cases in public, private, and social security healthcare facilities.  

WHO recommends strengthening epidemiological surveillance in high-traffic border areas to rapidly detect and respond to highly suspected measles cases. Providing a rapid response to imported measles cases to avoid the re-establishment of endemic transmission through the activation of rapid response teams trained for this purpose and by implementing national rapid response protocols when there are imported cases. Once a rapid response team has been activated, continued coordination between the national, sub-national, and local levels must be ensured, with permanent and fluid communication channels between all levels. During outbreaks, it is recommended to establish adequate hospital case management to avoid nosocomial transmission, with appropriate referral of patients to isolation rooms (for any level of care) and avoiding contact with other patients in waiting rooms and/or other hospital rooms.  

WHO recommends vaccination of at-risk populations (without proof of vaccination or immunity against measles and rubella), such as healthcare workers, persons working in tourism and transportation (hotels, airports, border crossings, mass transportation, and others), and international travelers. Implementing a plan to immunize migrant populations in high-traffic border areas, prioritizing those considered at-risk, including both migrants and residents, in these municipalities increases vaccination coverage to increase population immunity.  

In all settings, consideration should be given to providing susceptible contacts with post-exposure prophylaxis (PEP), including a dose of MCV or normal human immunoglobulin (NHIG) (if available) for those at risk and in whom the vaccine is contraindicated. In well-resourced settings, MCV should be provided to susceptible contacts within 3 days. For contacts for whom vaccination is contraindicated or is not possible within 3 days post-exposure, consideration can be given to providing NHIG up to 6 days post-exposure. Infants, pregnant women, and the immunocompromised should be prioritized.  

WHO recommends maintaining a stock of the MR and/or measles, mumps, rubella (MMR) vaccine, and syringes/supplies for control actions of imported cases. Facilitating access to vaccination services according to the national scheme to those from other countries or people from the same country who perform temporary activities in countries with ongoing outbreaks; displaced populations; indigenous populations, or other vulnerable populations.  

WHO does not recommend any restriction on travel and trade based on the information available on the current outbreak.  

Further information

-- World Health Organization. Measles [Internet]. Geneva: World Health Organization; [cited 2026 Apr 6]. Available from: https://www.who.int/health-topics/measles 

-- World Health Organization. Measles fact sheet [Internet]. Geneva: World Health Organization; 2025 Nov 28 [cited 2026 Apr 6]. Available from: https://www.who.int/news-room/fact-sheets/detail/measles  

-- World Health Organization. Immunization dashboard [Internet]. Geneva: World Health Organization; [cited 2026 Apr 6]. Available from: https://immunizationdata.who.int/  

-- World Health Organization. Measles outbreak guide [Internet]. Geneva: World Health Organization; 2022 Aug 31 [cited 2026 Apr 6]. Available from: https://www.who.int/publications/i/item/9789240052079  

-- Directorate General of Health Services (Bangladesh). Press releases [Internet]. Dhaka; [cited 2026 Apr 6]. Available from: https://dghs.gov.bd/pages/press-releases/  

-- Measles vaccines: WHO position paper – April 2017; https://www.who.int/publications/i/item/who-wer9217-205-227

-- Measles: Vaccine Preventable Diseases Surveillance Standards; https://www.who.int/publications/m/item/vaccine-preventable-diseases-surveillance-standards-measles

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Citable reference: World Health Organization (23 April 2026). Disease Outbreak News: Measles in Bangladesh. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2026-DON598

Source: 

Link: https://www.who.int/emergencies/disease-outbreak-news/item/2026-DON598

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