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Influenza Season 2024-25

Influenza is caused by influenza A or B viruses and occurs in annual winter epidemics. The surface molecules of the virus are constantly changing, which often results in a lack of immunity between seasons and requires vaccines to be updated each season. Twice a year, the World Health Organization (WHO) therefore recommends which vaccine antigens should be included in the season’s vaccine. For the Northern Hemisphere, this selection is made in February, based on surveillance of circulating influenza strains globally.

In recent years, the vaccine has been quadrivalent, providing protection against two subtypes of influenza A (A/H1N1pdm09 and A/H3N2) and two lineages of influenza B (B/Victoria and B/Yamagata). However, influenza B/Yamagata has not been identified globally since March 2020, and WHO now recommends a trivalent vaccine that does not include influenza B/Yamagata. Otherwise, the strains for influenza A have been updated, while the influenza B lineage/Victoria remains the same as the previous year.

The specific influenza strains included in the vaccine vary depending on how the vaccine has been manufactured.

The most common vaccine type consists of inactivated, split virus particles grown in eggs. This year’s trivalent egg-based influenza vaccine contain hemagglutinin derived from:

An alternative is cell culture-based inactivated vаϲϲiոеs, which are egg protein-free and may be suitable for individuals with severe egg allergies. This year’s trivalent cell culture-based influenza vaccine contains:

The quadrivalent vaccine also includes the B/Phuket/3073/2013-like virus (B/Yamagata lineage), which remains unchanged from previous years.

Vаϲϲiոatiοn is associated with a reduced incidence of iոflսenzа, but the effectiveness of this season’s vaccine is still uncertain. As with every year, there is a chance that mismatches between the vaccine strains and circulating strains could reduce its efficacy.

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