2026 Flu Strains

Influenza (Flu) viruses are constantly evolving and changing. The annual vaccine strains need to change to best match the currently circulating virus strains.

The World Health Organisation (WHO) recommends strains for our Southern Hemisphere vaccine annually, based on international surveillance of circulating viruses. Australasian experts then review our local data and epidemiology and agree on which strains will be in the upcoming vaccine.

WHO has recommended a trivalent (3 strain) vaccine rather than a quadrivalent (4 strain) vaccine this season as there has been no confirmed detection of the B/Yamagata lineage since March 2020.  

For the 2026 season both the A strains have changed from the 2025 strains.

The Trivalent vaccines for 2026 will be based on the following strains:

Egg-based vaccines 

A/Missouri/11/2025 (H1N1) pdm09-like virus;

A/Singapore/GP20238/2024 (H3N2) like virus; and

B/Austria/1359417/2021 (B/Victoria lineage)-like virus

Advanced / Cell-Based vaccines

A/Missouri/11/2025 (H1N1) pdm09-like virus;

A/Sydney/1359/2024 (H3N2) like virus; and

B/Austria/1359417/2021 (B/Victoria lineage)-like virus

The WHO recommend different strains for cell-based flu vaccine manufacture compared to egg-based manufacture.  This is because they select strains best suited to the production method.

Influenza viruses may not grow equally well in the egg- and cell-based vaccine production systems.  This means the WHO can recommend different viruses with similar properties for each of the two production systems.

The name of the strain comes from the site where the virus was first isolated.