Influenza viruses never stand still—mutating constantly as they spread across hemispheres and seasons. This biological restlessness challenges scientists and public health authorities to regularly reassess the match between circulating strains and seasonal vaccines. On Sept. 26, the World Health Organization (WHO) released its new recommendations for the composition of influenza vaccines for the 2026 southern hemisphere season. The guidance, based on extensive global surveillance and expert consultation, informs national health agencies, regulatory bodies, and manufacturers as they prepare vaccines for the upcoming season.
WHO’s semiannual consultations—one for each hemisphere—bring together specialists from the WHO Global Influenza Surveillance and Response System (GISRS), Collaborating Centres, and Essential Regulatory Laboratories. Over four days, the advisory group reviews global data on virus circulation, antigenic characteristics, and vaccine performance to update which strains should be targeted. These recommendations are more than scientific advice; they directly shape production pipelines worldwide, determining what goes into hundreds of millions of vaccine doses.
Key Updates to the 2026 Vaccine Composition
The 2026 southern hemisphere season will see a continued shift toward trivalent vaccines, reflecting WHO’s conclusion that the inclusion of a B/Yamagata lineage virus is no longer warranted—a decision consistent with previous recommendations since September 2023.
For trivalent vaccines, WHO recommends the following strains:
- A/Missouri/11/2025 (H1N1)pdm09-like virus
- A/Singapore/GP20238/2024 (H3N2)-like virus (egg-based) or A/Sydney/1359/2024 (H3N2)-like virus (cell-culture and recombinant platforms)
- B/Austria/1359417/2021 (B/Victoria lineage)-like virus
Where quadrivalent vaccines remain in use, they will still include the B/Phuket/3073/2013 (B/Yamagata lineage) strain; however, WHO will no longer issue updated recommendations for this lineage.
WHO has also highlighted updated candidate vaccine viruses for zoonotic influenza to strengthen pandemic preparedness, underscoring the link between seasonal vaccine composition and broader global health security strategies.
Implications for Public Health Security and National Interest
Accurate vaccine strain selection is a linchpin of seasonal influenza prevention and an essential pillar of national health security. A vaccine mismatch can lead to higher infection rates, increased hospitalizations, and greater strain on healthcare systems—effects that ripple into economies and national resilience. The latest recommendations demonstrate how robust global surveillance networks and evidence-driven decision-making protect not just vulnerable populations but also the continuity of workforce productivity and critical public services.
For the general public, these updates matter because effective vaccines reduce community transmission, protect individuals with underlying conditions, and help mitigate the risk that seasonal influenza could compound other respiratory disease outbreaks or overwhelm healthcare facilities.
Looking Ahead
The removal of B/Yamagata lineage signals a notable inflection point in vaccine strategy, reflecting the changing dynamics of influenza circulation. Public health and industry stakeholders will need to align manufacturing timelines, supply chains, and communication strategies to ensure smooth implementation of these changes. Additionally, the renewed emphasis on zoonotic influenza candidates highlights the intersection between seasonal influenza management and long-term pandemic preparedness planning.