The World Health Organization (WHO) has released its recommendations for the composition of influenza vaccines for the 2026-2027 northern hemisphere flu season, based on a four-day consultation held in late September 2025. The announcement follows a comprehensive review of global influenza surveillance data collected through the WHO Global Influenza Surveillance and Response System (GISRS), which monitors virus evolution year-round to inform vaccine updates. These biannual meetings are critical for aligning vaccine strains with those most likely to circulate during the upcoming flu season, aiming to maximize protection against severe illness, hospitalization, and death.
Influenza viruses mutate rapidly, necessitating regular updates to vaccine formulations to maintain effectiveness. For the 2026-2027 northern hemisphere season, WHO experts recommend that egg-based, cell culture-based, recombinant protein-based, and nucleic acid-based influenza vaccines all include specific strains designed to match the evolving antigenic profile of circulating viruses. The recommendations are used by national regulatory agencies and vaccine manufacturers worldwide to produce and license vaccines for the following season, ensuring global coordination in flu prevention efforts.
According to WHO Director-General Dr Tedros Adhanom Ghebreyesus, the process reflects the interconnected nature of global health: “Season after season, constantly evolving influenza viruses circulate globally, showing us how connected our world is. Shared risks require shared action.” He emphasized that the success of these recommendations relies on the continuous, year-round work of GISRS and its partners in tracking viral changes across human and animal populations.
For egg-based vaccines, WHO recommends the following three components: an A/Missouri/11/2025 (H1N1)pdm09-like virus; an A/Darwin/1454/2025 (H3N2)-like virus; and a B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like virus. For cell culture-, recombinant protein-, or nucleic acid-based vaccines, the recommended strains are: an A/Missouri/11/2025 (H1N1)pdm09-like virus; an A/Darwin/1415/2025 (H3N2)-like virus; and a B/Pennsylvania/14/2025 (B/Victoria lineage)-like virus. The slight variation in the H3N2 component between vaccine platforms reflects differences in how viruses propagate in egg-based versus mammalian cell systems, which can affect antigenic fidelity.
The selection of these strains was informed by surveillance data showing that in August 2025, a notable variant of the A(H3N2) virus emerged, classified as clade J.2.4.1 and commonly referred to as subclade K. This variant spread rapidly across multiple continents and contributed to an earlier onset of influenza activity in several countries, with higher-than-usual levels of viral detection reported during surveillance weeks. Subclade K viruses accounted for the majority of A(H3N2) sequences submitted to GISRS from regions including Southeast Asia, Europe, and North America during the second half of 2025.
Influenza A viruses continued to dominate global circulation during the surveillance period, with both A(H1N1)pdm09 and A(H3N2) subtypes detected. In contrast, influenza B viruses were predominantly of the B/Victoria lineage, with very low levels detected and no confirmed cases of B/Yamagata lineage viruses since March 2020. The apparent absence of B/Yamagata circulation has led to ongoing discussion about whether this lineage should remain included in quadrivalent vaccines, though WHO continues to recommend its inclusion for now as a precaution against potential re-emergence.
As part of the zoonotic influenza risk assessment, experts reviewed avian and swine influenza viruses that have caused sporadic human infections. Since the previous consultation on 23 September 2025, 25 human cases of zoonotic influenza were reported to WHO from six countries: Cambodia, China, Egypt, India, Vietnam, and Zambia. All cases were linked to direct or indirect exposure to infected poultry or contaminated environments, with no evidence of sustained human-to-human transmission. The majority were associated with A(H5N1) and A(H9N2) viruses, underscoring the ongoing pandemic threat posed by animal influenza reservoirs.
In response to the evolving zoonotic risk landscape, the consultation also recommended the development of a new candidate vaccine virus (CVV) for an A(H9N2) avian influenza strain. This preparatory step ensures that if an A(H9N2) virus were to acquire enhanced transmissibility among humans, vaccine manufacturers could rapidly pivot production using established platforms. CVVs are standardized, high-yield virus strains used by manufacturers to accelerate vaccine development during emerging threats.
Global influenza surveillance has been conducted through GISRS since 1952, making it the longest-running international system for monitoring infectious diseases. The network includes over 150 national influenza centers in more than 120 countries, six WHO Collaborating Centres, and Essential Regulatory Laboratories that jointly analyze viral samples, assess antigenic properties, and monitor antiviral susceptibility. This infrastructure enables timely detection of drift and shift in influenza viruses, supporting both seasonal vaccine updates and pandemic preparedness.
Seasonal influenza remains a significant global health burden, with the WHO estimating up to 1 billion infections annually worldwide, including 3 to 5 million cases of severe illness. Respiratory deaths linked to seasonal flu are estimated to range between 290,000 and 650,000 each year, disproportionately affecting older adults, young children, pregnant individuals, and those with underlying chronic conditions. Vaccination remains the most effective tool for reducing severe outcomes, particularly when administered before the onset of community transmission.
Public health officials in the northern hemisphere recommend that individuals receive their annual flu vaccine by the finish of October, ideally before flu activity begins to increase in communities. Vaccines are widely available through doctors’ offices, pharmacies, public health clinics, and workplace or school-based programs. In the United States, the Centers for Disease Control and Prevention (CDC) provides a vaccine finder tool at Vaccines.gov, while in Europe, the European Centre for Disease Prevention and Control (ECDC) supports national immunization programs through guidance and surveillance coordination.
Manufacturers typically begin distributing northern hemisphere flu vaccines in August and September, with supplies continuing through November or until inventory is depleted. Early vaccination is especially encouraged for high-risk groups and caregivers of vulnerable individuals. While vaccine effectiveness varies from season to season depending on the match between vaccine strains and circulating viruses, even imperfect matches can reduce the risk of severe disease, hospitalization, and death.
Looking ahead, the next WHO consultation on influenza vaccine composition will seize place in February 2026 to determine recommendations for the 2026-2027 southern hemisphere influenza season. This meeting will again rely on the latest GISRS data to assess viral evolution and antigenic trends during the northern hemisphere’s peak flu months. Stakeholders including national immunization technical advisory groups (NITAGs), vaccine producers, and public health agencies will use the southern hemisphere recommendations to guide procurement and planning for the following year.
Staying informed about flu vaccine updates helps individuals and healthcare providers make timely decisions about protection. For the most current information on influenza surveillance, vaccine recommendations, and public health guidance, refer to the WHO Influenza website or national public health agencies such as the CDC, ECDC, or your local health department.
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