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 2022-2023 were endorsed by EMA’s human medicines committee (CHMP) at its March 2022 meeting.

Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate in all parts of the world. It represents a year-round disease burden. It causes illnesses that range in severity and sometimes lead to hospitalization and death.

Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe illness or death, particularly among high risk groups including the very young, the elderly, pregnant women, health workers and those with serious medical conditions.

There are 4 types of seasonal influenza viruses, types A, B, C and D. Influenza A and B viruses circulate and cause seasonal epidemics of disease.

• Influenza A viruses are further classified into subtypes according to the combinations of the hemagglutinin (HA) and the neuraminidase (NA), the proteins on the surface of the virus. Currently circulating in humans are subtype A(H1N1) and A(H3N2) influenza viruses. The A(H1N1) is also written as A(H1N1)pdm09 as it caused the pandemic in 2009 and subsequently replaced the seasonal influenza A(H1N1) virus which had circulated prior to 2009. Only influenza type A viruses are known to have caused pandemics.
• Influenza B viruses are not classified into subtypes, but can be broken down into lineages. Currently circulating influenza type B viruses belong to either B/Yamagata or B/Victoria lineage.
• Influenza C virus is detected less frequently and usually causes mild infections, thus does not present public health importance.
• Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

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.

EMA has issued the recommendations for the influenza virus strains that vaccine manufacturers of egg-based or live attenuated, cell-based quadrivalent vaccines for the 2022-2023 season should include these four virus strains:

• an A/Victoria/2570/2019 (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.

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. More information on EMA.