Selecting Viruses for the Seasonal Influenza Vaccine

Summary

Seasonal influenza (flu) vaccines are designed to protect against the three main groups of flu Type A and B viruses that research indicates are most likely to spread and cause illness among people during the upcoming flu season. All current U.S. flu vaccines protect against an influenza A(H1N1) virus, an influenza A(H3N2) virus, an influenza B/Victoria lineage virus. Each of these three vaccine virus components are selected based on the following:

• Which influenza viruses are making people sick prior to the upcoming flu season,
• The extent to which those viruses are spreading prior to the upcoming flu season,
• How well the previous season's vaccines may protect against those influenza viruses, and
• The ability of vaccine viruses to provide cross-protection against a range of related influenza viruses of the same type or subtype/lineage.

There are currently 152 national influenza centers (NICs) in over 129 countries that conduct year-round surveillance for flu viruses as part of the World Health Organization (WHO) Global Influenza Surveillance and Response System (GISRS). This involves receiving and testing thousands of influenza virus samples from patients. For human seasonal flu surveillance, the laboratories send representative viruses to 5* of the 7 WHO Collaborating Centers for Influenza, which are located in the following places:

• Atlanta, Georgia, USA (Centers for Disease Control and Prevention, CDC)
• Memphis, Tennessee, USA (St. Jude Children's Research Hospital)
• London, United Kingdom (The Francis Crick Institute)
• Melbourne, Australia (Victoria Infectious Diseases Reference Laboratory)
• Tokyo, Japan (National Institute for Infectious Diseases)
• Beijing, China (National Institute for Viral Disease Control and Prevention)
• Koltsovo, Russian Federation (State Research Center of Virology and Biotechnology "VECTOR," Rospotrebnadzor)

*Note: Two of the WHO Collaborating Centers—the one in Memphis, Tennessee, and the one in Koltsovo, Russian Federation—only collect influenza virus specimens from animals and do not participate in human seasonal flu surveillance.

Twice a year, the WHO organizes a consultation with the Directors of the seven WHO Collaborating Centers, Essential Regulatory Laboratories, and representatives of key national laboratories and academies. They review the results of surveillance, laboratory, and clinical studies, and the availability of flu vaccine viruses and make recommendations on the composition of flu vaccines. These meetings take place in February for selection of the upcoming Northern Hemisphere's seasonal flu vaccines and in September for the Southern Hemisphere's flu vaccines. The WHO vaccine composition committee, which is comprised of independent technical advisors (i.e., directors of each of the WHO Collaborating Centers and Essential Regulatory Laboratories (ERLs), meets to present global flu data and recommend specific vaccine viruses for flu vaccines. Next, each country makes its own decision about which viruses should be included in flu vaccines licensed in their country.

In the United States, the Food and Drug Administration (FDA)'s Vaccines and Related Biological Products Advisory Committee (VRBPAC) makes the final decision about which vaccine viruses to include in the composition of domestic flu vaccines. Information about the circulation of influenza viruses and available vaccine viruses is summarized and presented to VRBPAC in February or March of each year for the U.S. decision about which viruses to include in the upcoming season's flu vaccine.