Vaccine Selection for the 2011-2012 and 2012-2013 Influenza Seasons

Questions & Answers

Each year, experts from FDA, WHO, U.S. Centers for Disease Control and Prevention (CDC) and other institutions study virus samples collected from around the world to identify the influenza viruses that are the most likely to cause illness during the upcoming flu season so that people can be protected against them through vaccination.

On February 23, 2012 the World Health Organization (WHO) recommended that the Northern Hemisphere's 2012-2013 seasonal influenza vaccine contain the following three vaccine viruses:

• an A/California/7/2009 (H1N1)pdm09-like virus;
• an A/Victoria/361/2011 (H3N2)-like virus;
• a B/Wisconsin/1/2010-like virus (from the B/Yamagata lineage of viruses).

While the H1N1 virus is the same, the H3N2 and B vaccine viruses are different from those that were selected for the Northern Hemisphere for the 2011-2012 influenza vaccine.

The WHO also recommended for those countries considering including two influenza B viruses in their vaccine, that a B/Brisbane/60/2008-like virus (from the B/Victoria lineage of viruses) be used.

During February 2012 the U.S. Food and Drug Administration (FDA) Vaccines and Related Biological Products Advisory Committee (VRBPAC) will meet to discuss the WHO recommendation. They will make a final decision for the composition of influenza vaccine that will be used in the United States for the 2012-2013 season.

The WHO Vaccine Composition Meeting was held February 21-23, 2012 at the WHO headquarters in Geneva, Switzerland. A detailed report [408 KB, 16 pages] is available on the WHO web site.

How are the viruses selected to make flu vaccine?

The influenza (flu) viruses selected for inclusion in the seasonal flu vaccines are updated each year based on information about which influenza viruses are being found, how they are spreading, and how well the previous season's vaccine viruses might protect against any that are being newly identified. Currently, over 100 national influenza centers in over 100 countries conduct year-round surveillance for influenza viruses and disease activity. These laboratories then send influenza viruses for additional analyses to the 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).

Since the early 1980s, the seasonal flu vaccine has been trivalent (a three-component vaccine) with each component selected to protect against one of the three main groups of influenza viruses circulating in humans.

Three vaccine viruses are chosen to maximize the likelihood that the influenza vaccine will protect against the viruses most likely to spread and cause illness among people during the upcoming flu season. WHO recommends specific vaccine viruses for influenza vaccine production, but then individual countries make their own decisions for licensing of vaccines in their country. In the United States, the U.S. Food and Drug Administration determines what viruses will be used in U.S.-licensed vaccines.

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Who is included in the group that makes the vaccine virus selections at WHO?

The WHO vaccine virus decision meetings include WHO representatives from the WHO Collaborating Centers, Essential Regulatory Laboratories, and others from the Global Influenza Surveillance Network (GISN). After WHO makes its recommendations, the U.S. FDA Vaccines and Related Biological Products Advisory Committee (VRBPAC) meets to concur with or modify WHO's recommendation for the United States.

What flu viruses are included in the Northern Hemisphere seasonal vaccine for 2011-2012?

The Northern Hemisphere's 2011—2012 seasonal influenza vaccine contains the following three vaccine viruses:

• an A/California/7/2009 (H1N1)-like virus;
• an A/Perth/16/2009 (H3N2)-like virus; and
• a B/Brisbane/60/2008-like virus.

These are the same viruses that were selected for the Northern Hemisphere for the 2010-2011 influenza vaccine.

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When and where did the WHO group meet to determine the vaccine composition for the 2011-2012 seasonal influenza vaccine for the Northern Hemisphere?

On January 10 and January 27, 2011, the WHO selection process for which viruses to include in the seasonal influenza vaccine for the Northern Hemisphere began with teleconferences discussing influenza surveillance data. 

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When and where was it decided what the vaccine composition would be for the 2011-2012 seasonal vaccine for the United States?

After WHO made its recommendations for the Northern Hemisphere, the U.S. FDA Vaccines and Related Biological Products Advisory Committee (VRBPAC) met in Bethesda, Maryland on February 25, 2011 and concurred with WHO's recommendation. So the U.S. seasonal vaccine for the 2011-2012 season includes an A/California/7/2009 (H1N1)-like virus, an A/Perth/16/2009 (H3N2)-like virus, and a B/Brisbane/60/2008-like virus.

What flu viruses are included in the Southern Hemisphere seasonal vaccine for 2011?

On September 29, 2010, in Geneva, Switzerland, WHO recommended that the Southern Hemisphere's seasonal influenza vaccine contain the following three vaccine viruses:

• an A/California/7/2009 (H1N1)-like virus;
• an A/Perth/16/2009 (H3N2)-like virus;* and
• a B/Brisbane/60/2008-like virus.

*Note: A/Wisconsin/15/2009 and A/Victoria/210/2009 are A/Perth/16/2009-like viruses.

The WHO recommendation and summary report are available on the WHO website. In addition, a frequently asked questions document [66 KB, 2 pages] on the vaccine strain selection process is also available on the WHO website.

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When the influenza vaccine composition is the same for the upcoming season as it was for the previous season, do I need to get vaccinated again?

Yes. People should get vaccinated every year because even if the viruses in the vaccine are the same as the year before, immunity to influenza viruses declines over time and may be too low to provide protection after a year. More information is available about the frequency and timing of flu vaccination.

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