EMA has issued the recommendations for the influenza virus strains1,2  that vaccine manufacturers should include in vaccines for the prevention of seasonal influenza from autumn 2023.

Manufacturers of egg-based or live attenuated quadrivalent vaccines for the 2023-2024 season should include these four virus strains:

  • an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
  • an A/Darwin/9/2021 (H3N2)-like virus;
  • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
  • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Manufacturers of cell-based quadrivalent vaccines for the 2023-2024 season should include these four virus strains:

  • an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
  • an A/Darwin/6/2021 (H3N2)-like virus;
  • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
  • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

For vaccine manufacturers considering the use of one B lineage vaccine virus only in trivalent vaccines, a B/Austria/1359417/2021 (B/Victoria lineage)-like virus is considered appropriate for inclusion. Therefore, a B/Yamagata lineage virus is not recommended for inclusion in trivalent vaccines.

These recommendations apply to the manufacture of both inactivated and live attenuated influenza vaccines.

Every year, EMA's ad hoc Influenza Working Group issues EU recommendations for the composition of seasonal influenza vaccines on the basis of observations by the World Health Organization. The recommendations for the influenza season 2023-2024 were endorsed by EMA's human medicines committee (CHMP) at its March 2023 meeting.

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.

The Agency recommends that marketing authorisation holders submit applications to change the composition of centrally authorised seasonal flu vaccines by 12 June 2023.

Revision 2 of the Guideline on influenza vaccines – submission and procedural requirements (Rev.2) is also published. This includes minor updates to the Product Information (Annex II) of the guideline including changes made to reflect current practice.

1 The news announcement was updated on 4 April 2023 to include a fourth virus strain.

2 This news announcement includes the information from the EU recommendation for the seasonal influenza vaccine composition for the season 2023/2024 which were amended subsequent to CHMP adoption on 14 April 2023. Please refer to the linked document which specifies the additional strain added on 14 April. Annex I of the recommendation (Reagents for vaccine standardisation) has also been updated.

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