2026 Southern Hemisphere Influenza Vaccine Composition

The World Health Organisation confirmed on 26 September 2025 the recommended influenza vaccine strains for the 2026 Southern Hemisphere season. These recommendations directly shape the vaccines used during the New Zealand Flu Season.

Influenza viruses change every year. Small genetic changes can make the virus harder for our immune system to recognise. Because of this, the flu vaccine is reviewed and updated annually. This is why we recommend vaccination each year, even if you received one last winter.

For the 2026 New Zealand Flu Season, WHO recommends the following strains:

Cell based vaccines for 2026 include:

• an A/Missouri/11/2025 (H1N1)pdm09-like virus;
• an A/Sydney/1359/2024 (H3N2)-like virus; and
• a B/Austria/1359417/2021 (B/Victoria lineage)-like virus

Cell based vaccines are produced using cultured mammalian cells rather than fertilised chicken eggs. This method avoids egg adaptation changes and may improve how closely the vaccine matches the circulating virus, particularly for H3N2 strains.

Egg based vaccines for 2026 include:

• an A/Missouri/11/2025 (H1N1)pdm09-like virus;
• an A/Singapore/GP20238/2024 (H3N2)-like virus; and
• a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.

Egg based vaccines have been safely used for more than 70 years. They remain an effective and well established option for protecting people during the New Zealand Flu Season.

The key difference between the two vaccine types this year is the H3N2 component. This reflects how each virus strain grows in the manufacturing process. Both vaccine types protect against three main influenza strains expected to circulate.

Why B Yamagata Is No Longer Included

WHO continues to advise that a B Yamagata lineage strain is no longer required in routine influenza vaccines. Surveillance data shows this strain has not circulated globally for several seasons. Some quadrivalent vaccines may still include a fourth B Yamagata strain while countries transition to trivalent vaccines.

Why Vaccine Strains Change Each Year

The 2026 vaccine strains differ from those used in 2025, and they also differ from the strains recommended for the 2025 to 2026 Northern Hemisphere season. This change is deliberate. Influenza viruses are unstable by nature. They undergo frequent genetic changes through processes known as antigenic drift. These small mutations can alter surface proteins on the virus, particularly haemagglutinin and neuraminidase, which are the main targets of our immune response. Even minor changes can reduce how well immunity from a previous infection or vaccination recognises the virus the following year.

Because of this constant viral evolution, the World Health Organisation carries out global influenza surveillance throughout the year. More than 150 national influenza centres across over 100 countries collect respiratory samples. Laboratories sequence viruses, identify emerging variants, and share findings through the Global Influenza Surveillance and Response System. Hospital data is reviewed to assess severity, age distribution, and complication rates. Public health agencies also analyse vaccine effectiveness from the most recent season to understand how well protection held up against circulating strains.

Twice a year, technical advisory groups meet to review this data. In late September, WHO issues its formal recommendation for the Southern Hemisphere influenza vaccine composition. This timing is critical. Most influenza vaccines require six to eight months for regulatory approval, large scale manufacturing, quality control testing, packaging, and global distribution. Manufacturers must grow and process vaccine viruses, confirm stability and safety, and prepare hundreds of millions of doses for countries including New Zealand.

This structured timeline ensures vaccines are available before the New Zealand Flu Season begins, which typically runs from May through September, with peak transmission in winter. Without annual updates to vaccine composition, protection would gradually weaken as circulating strains drift further from older vaccine strains. Regular reformulation remains essential to maintain vaccine effectiveness, reduce hospitalisation, and protect public health both in New Zealand and worldwide.

What This Means for You

The annual update process is designed to give New Zealanders the best possible protection against influenza each winter. Flu vaccination reduces the risk of severe illness, hospitalisation, and complications such as pneumonia. It also reduces the likelihood of spreading influenza to vulnerable people, including older adults, pregnant women, young children, and those with chronic medical conditions.

Even in seasons where circulating strains vary slightly from predictions, vaccination remains the most effective tool we have to reduce serious outcomes.

WHO recommendations form the basis for national regulatory approvals and vaccine supply planning worldwide. Regular strain updates are essential for maintaining vaccine effectiveness and protecting public health during every New Zealand Flu Season.

For full technical details, read the WHO report (dated 26 September 2025) linked here.