Yearly updates of influenza vaccines

An update of seasonal influenza vaccines is needed yearly, since influenza viruses constantly evolve. How effective the seasonal influenza vaccine is each season depends on the match between the selected vaccine viruses and those found circulating, and will therefore vary from year to year.

In order to find the best match and increase the vaccine effectiveness, experts meet each February/March to review the precise influenza strains to include in the forthcoming season’s vaccine to be used in the northern hemisphere. This process is managed by the World Health Organization (WHO).

The WHO influenza strain selection meeting engages specialists who review relevant virological, epidemiological, immunological and vaccine performance information in the last seasons for the northern and southern hemispheres. Based on this review, new WHO influenza vaccine strain recommendations for the updated vaccines for the forthcoming season are agreed upon.