The World Health Organization (WHO) has announced its recommendations for the composition of influenza vaccines for the 2026-2027 northern hemisphere influenza season. This crucial step, based on a four-day consultation examining global influenza surveillance data, aims to ensure that vaccines are optimally matched to circulating viruses, offering the best possible protection against severe illness, and death. The ongoing need to update vaccine composition stems from the constant evolution of influenza viruses, a challenge that necessitates continuous monitoring and adaptation.
These recommendations aren’t simply suggestions; they are pivotal for guiding national vaccine regulatory agencies and pharmaceutical companies worldwide in the development, production, and licensing of influenza vaccines for the upcoming season. The WHO’s Global Influenza Surveillance and Response System (GISRS) plays a central role in this process, providing the data-driven insights that inform these critical decisions. Understanding the evolving landscape of influenza is paramount, especially given the potential for severe health impacts and the interconnectedness of global health security.
A significant factor influencing the 2026-2027 vaccine recommendations was the emergence of a distinct variant of the A(H3N2) virus in August 2025, classified as J.2.4.1, also referred to as “subclade K.” This variant spread rapidly across the globe and contributed to an earlier-than-usual start to the influenza season in many countries, with several regions reporting higher-than-usual levels of activity. According to the WHO, ‘subclade K’ accounted for the majority of influenza viruses reported across regions during this period.
influenza A viruses were predominant, with other variants of A(H3N2) and A(H1N1) also recorded. Levels of influenza B viruses (B/Victoria lineage) remained low, and no cases of B/Yamagata lineage viruses have been reported since March 2020. The WHO also continues to monitor zoonotic influenza viruses, including “bird flu,” which pose a pandemic threat. Since September 23, 2025, 25 human infections with zoonotic influenza have been reported from six countries, though no human-to-human transmission has been observed.
Recommended Vaccine Composition for 2026-2027
The WHO’s recommendations specify different viral strains for egg-based and cell culture-based vaccines. For egg-based vaccines, the recommended strains are:
- An A/Missouri/11/2025 (H1N1)pdm09-like virus
- An A/Darwin/1454/2025 (H3N2)-like virus
- A B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like virus
For cell culture-, recombinant protein- or nucleic acid-based vaccines, the recommendations are:
- An A/Missouri/11/2025 (H1N1)pdm09-like virus
- An A/Darwin/1415/2025 (H3N2)-like virus
- A B/Pennsylvania/14/2025 (B/Victoria lineage)-like virus
These biannual meetings, bringing together experts from the WHO’s Collaborating Centres and Essential Regulatory Laboratories of the GISRS, are critical for assessing circulating viruses and selecting new candidate vaccine viruses (CVVs) that can be rapidly used to manufacture vaccines should a pandemic threat arise. At this recent meeting, experts recommended the development of a new CVV for an A(H9N2) virus.
The Ongoing Threat of Influenza
Seasonal influenza remains a significant public health concern globally. The WHO estimates that around one billion cases of seasonal influenza occur annually, resulting in 3–5 million cases of severe illness and an estimated 290,000 to 650,000 respiratory deaths each year (WHO). The organization’s Global Influenza Surveillance and Response System (GISRS), established in 1952, represents the longest-standing global platform for systematic disease surveillance.
“Season after season, constantly evolving influenza viruses circulate globally, showing us how connected our world is. Shared risks require shared action,” said Dr. Tedros Adhanom Ghebreyesus, WHO Director-General. This sentiment underscores the importance of international collaboration and proactive measures in mitigating the impact of influenza.
Looking ahead, continued vigilance and robust surveillance efforts will be essential to track the evolution of influenza viruses and ensure the effectiveness of seasonal vaccines. The development of new CVVs, like the one recommended for the A(H9N2) virus, demonstrates the ongoing commitment to pandemic preparedness. The WHO will continue to monitor influenza activity globally and provide updated recommendations as needed.
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Disclaimer: This article provides informational content about influenza and vaccine recommendations and should not be considered medical advice. Please consult with a qualified healthcare professional for personalized guidance on influenza prevention and treatment.
