Recommendations for influenza vaccines

Why annual recommendations for influenza vaccine composition are necessary

Circulating influenza viruses in humans are subject to permanent antigenic changes which require annual adaptation of the influenza vaccine formulation. Updates in influenza vaccine composition should ensure the closest possible match between the influenza vaccine strains and the circulating influenza strains; ensuring this match is one of the foundations for influenza vaccine efficacy.

Participants at the WHO Consultation on the Composition of Influenza Vaccine for the Southern Hemisphere 2007

How they are made

Information on circulating strains and epidemiological trends is gathered by the WHO Global Influenza Surveillance Network administered by WHO since 1948, the year of WHO’s inception. The Global Influenza Surveillance Network currently consists of 128 National Influenza Centres in 99 countries and four WHO Collaborating Centres for Reference and Research on Influenza located in Atlanta, United States; London, United Kingdom; Melbourne, Australia; and Tokyo, Japan.

The National Influenza Centres sample patients with influenza-like illness and submit representative isolates to WHO Collaborating Centres for immediate strain identification. In addition to genetic and antigenic analyses of influenza viruses, the WHO CCs jointly with key national laboratories involved in registration and quality control of influenza vaccines (Australia, United Kingdom, United States) collaborate annually on serological studies to obtain evidence as to whether the current vaccines induce satisfactory antibody levels to new epidemic strains.

Twice a year, WHO organizes a consultation with the Directors of the WHO Collaborating Centres and representatives of key national laboratories to review the results of these laboratory and clinical studies and make recommendations on the composition of the influenza vaccine (February: northern hemisphere; September: southern hemisphere). Immediately after this consultation WHO informs representatives of pharmaceutical companies on its decisions which are published in the press and the WHO Weekly Epidemiological Record. WHO collaborates with key national licensing agencies on the provision of viruses for vaccine production as well as vaccine potency testing reagents. More than 250 million vaccine doses are produced annually based on the WHO recommendations. Since 1972 WHO has recommended 39 changes in the influenza vaccine formulation.

Geographic distribution of National Influenza Centres

Legend: /White: No laboratory/ Blue: One laboratory/Dark blue: More than one laboratory