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Selecting Viruses for the Seasonal Influenza Vaccine

The seasonal influenza vaccine is designed to protect against the influenza viruses research indicates are most likely to spread and cause illness among people during the upcoming flu season. Flu viruses are constantly changing, so the vaccine is updated each year based on which influenza viruses are making people sick, how those viruses are spreading, and how well the previous season’s vaccine protects against those viruses.

More than 100 national influenza centers in over 100 countries conduct year-round surveillance for influenza. This involves receiving and testing thousands of influenza virus samples from patients with suspected flu illness. The laboratories send representative viruses to five World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza, which are located in the following places:

  • Atlanta, Georgia, USA (Centers for Disease Control and Prevention, CDC);
  • London, United Kingdom (National Institute for Medical Research);
  • Melbourne, Australia (Victoria Infectious Diseases Reference Laboratory);
  • Tokyo, Japan (National Institute for Infectious Diseases); and
  • Beijing, China (National Institute for Viral Disease Control and Prevention).

In February of each year, WHO consults with experts from WHO Collaborating Centers, Essential Regulatory Laboratories, and other partners to review data generated by the worldwide network of influenza laboratories. Afterward, WHO makes recommendations for the composition of the seasonal influenza vaccine for the Northern Hemisphere.

The U.S. Vaccines and Related Biological Products Advisory Committee (VRBPAC) - which is a part of the U.S. Food and Drug Administration (FDA) – considers the WHO recommendations and makes a final decision regarding composition of seasonal flu vaccine for the United States.

2014-2015 Influenza Vaccine Composition

The vaccine viruses recommended by WHO for the 2014-15 northern hemisphere influenza season are the same as those for the northern hemisphere 2013-14 influenza season and 2014 southern hemisphere season.

The WHO Vaccine Composition Meeting for the 2014-2015 season was held February 17 -19, 2014 at WHO headquarters in Geneva, Switzerland. On February 20, the Meeting recommended that trivalent vaccines for use in the Northern Hemisphere 2014-15 influenza season contain the following:

  • an A/California/7/2009 (H1N1)pdm09-like virus;
  • an A/Texas/50/2012 (H3N2)-like virus;
  • a B/Massachusetts/2/2012-like virus.

The Meeting also recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Brisbane/60/2008-like virus.

For more information about these WHO recommendations, see Questions and Answers.

Later this month, VRBAC will meet and decide for the United States the composition for the Northern Hemisphere 2014-2015 influenza vaccine.

The WHO Vaccine Composition Meeting for Southern Hemisphere 2014 influenza season vaccines was held September 23-26, 2013, at WHO headquarters in Geneva, Switzerland. The recommended composition is the same as the composition of 2013-2014 Northern Hemisphere vaccines.

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