Every year, EMA issues EU recommendations for the composition of seasonal influenza vaccines on the basis of observations by the World Health Organization (WHO), which are informed by regular monitoring activities on the prevalence and characteristics of different influenza viruses worldwide.

Manufacturers of live-attenuated vaccines or egg-based vaccines should include these three virus strains for the 2026/2027 season:

• 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.

Manufacturers of cell-based vaccines should include these three virus strains for the 2026/2027 season:

• 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.

Previously, most authorised influenza vaccines were formulated to protect against the four main strains of influenza responsible for seasonal flu, including the strain known as B/Yamagata.

However, since B/Yamagata has not been detected in circulation since March 2020, it is considered to no longer pose a threat to public health. As a result, there is no EU recommendation for a B/Yamagata strain in seasonal influenza vaccines for the 2026/2027 influenza season, which is in line with the respective WHO recommendation regarding the composition of vaccines for 2026/2027.
In case quadrivalent vaccines are still required (e.g. in regions where the transition to trivalent vaccines has not been finalised yet), vaccine manufacturers of inactivated vaccines can consider producing a quadrivalent vaccine containing two influenza B virus strains for the 2026/2027 season. For these vaccines it is proposed to follow WHO recommendations from previous years for the B/Yamagata strain, i.e. a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Influenza viruses continuously change and evolve. The periodic replacement of the virus strains contained in influenza vaccines is therefore necessary to keep the vaccines effective.

Influenza viruses continuously change and evolve. That is why it is necessary to review the virus strains contained in influenza vaccines and, if necessary, update them before the new flu season.

Every year, the European Medicines Agency (EMA) issues recommendations for the composition of seasonal influenza vaccines well in advance of flu season, giving manufacturers time to begin production. Some years, there is not change; other years, one or two of the strains are replaced.

The regulator advises companies which strains of flu viruses they should protect against when formulating the revamped vaccine. This is based on WHO data which draws on the experience of the southern hemisphere, where flu season is just beginning.

Based on this data, the EMA’s Emergency Task Force recommends moving from a four-strain vaccine to a three-strain vaccine which does not include the B/Yamagata component featured in recent years. This is because that flu virus has not been very common recent flu seasons, north or south.

In fact, it has not been detected since March 2020, when COVID-19 was declared a global pandemic. This is thought to be due in part to the public health measures put in place to limit the spread of COVID. Influenza B viruses are responsible for a quarter of annual influenza infections.

Given that the B-Yamagata virus strain no longer seems to pose a threat to public health, it is not necessary to include it in the formulation of influenza vaccines, the EMA said.

The ETF recommends that this strain should ideally be removed from all live-attenuated vaccines from the 2024/2025 season. In the interest of guaranteeing vaccine supplies for the coming vaccination campaign, the transition to a trivalent composition for all other influenza vaccines should be completed for the 2025/2026 season.

On foot of this, the following strains are now the priority for the 2024/2025 season.

Manufacturers of live-attenuated vaccines, or egg-based trivalent vaccines should include:

• an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
• an A/Thailand/8/2022 (H3N2)-like virus;
• a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.

Manufacturers of cell-based trivalent vaccines should include:

• an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
• an A/Massachusetts/18/2022 (H3N2)-like virus;
• a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.