How is it decided which strains should be included in the vaccine each year?
The World Health Organization (WHO) makes recommendations about which strains should be included in influenza vaccines each influenza season. There are two seasons each year, the Northern Hemisphere season and the Southern Hemisphere season.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 112 national influenza centres in 83 countries and four WHO Collaborating Centres for Reference and Research on Influenza (WHO CC) located in Atlanta, United States; London, United Kingdom; Melbourne, Australia; and Tokyo, Japan.The National Influenza Centres test samples from patients with influenza-like illness for strain identification,and submit representative isolates to WHO Collaborating Centres for genetic and antigenic analyses of influenza viruses.
