Flu vaccines to target three virus strains this autumn

Vaccine manufacturers have been tasked with producing vaccines that protect against three influenza viruses, as Europe gears up for another flu season. Companies are actively producing millions of doses to meet anticipated demand.

Based on data from the World Health Organization (WHO), the European Medicines Agency (EMA) selected the three most common strains of flu – a break from previous years in which four strains were targeted.

Influenza viruses continuously change and evolve. The periodic replacement of the virus strains contained in influenza vaccines is necessary to keep the vaccines effective. Every year, EMA issues recommendations for the composition of seasonal influenza vaccines based on trends seen last winter and monitoring data from the southern hemisphere flu season.

For 2024/2025, the Agency is recommending a transition from quadrivalent (four-strain) to trivalent (three-strain) vaccines that do not include the B/Yamagata component which was included last year. The B/Yamagata strain of the influenza B virus has not been detected in circulation since March 2020. This is thought to be due in part to the public health measures put in place to limit the spread of COVID-19 during the pandemic. Influenza B viruses are responsible for a quarter of annual influenza infections.

Manufacturers of live-attenuated vaccines, or egg-based trivalent vaccines should include these three virus strains for the 2024/2025 season:

• 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 these three virus strains for the 2024/2025 season:

• 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.

The EMA said manufacturers of inactivated vaccines can consider producing a quadrivalent vaccine containing two influenza B virus strains for the 2024/2025 season. ‘In that case a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus in addition to the strains mentioned above is considered appropriate,’ the Agency said in a statement.