CDC answers questions about vaccine selection for 2010-11 flu season

The Centers for Disease Control and Prevention recently addressed questions about the vaccine for the 2010-11 flu season on its Web site.

How are the viruses selected to make flu vaccine?

The viruses used in making seasonal flu vaccines are chosen each year based on information collected over the previous year about which flu viruses are spreading and causing the most illness.

Viruses gathered by 130 national influenza centers in 101 countries as well as information on disease trends are further analyzed by the five World Health Organization Collaborating Centers for Reference and Research on Influenza:  the CDC in Atlanta; London; Melbourne, Australia; Tokyo; and Beijing.

While there are many different flu viruses, the seasonal flu vaccine is usually a trivalent vaccine that protects against the three viruses that research suggests will be most common during the following season. The WHO also recommends specific virus strains that can be used for vaccine production. The 2009 H1N1 vaccine that was made to protect against the pandemic virus first detected in April only protected against the 2009 H1N1 viruses.

When and where will the group meet to determine the vaccine composition for the 2010-11 seasonal influenza vaccine?

The selection process of which influenza viruses will be used in the Northern Hemisphere 2010-11 seasonal influenza vaccine is under way. The final WHO Vaccine Composition Meeting will take place Feb. 14-19 at the WHO headquarters in Geneva.

Who is included in the group that will make the vaccine virus selections?

The group changes from year to year, but is composed of WHO representatives from the WHO Collaborating Centers, Essential Regulatory Labs and others from the Global Influenza Surveillance Network. After WHO makes its recommendations for the Northern Hemisphere, the Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee meets Feb. 22 in Bethesda, Md., to concur with or modify the WHO's recommendation for the United States.

How many flu viruses will be included in the seasonal vaccine for 2010-11?

In past years, seasonal influenza vaccines have contained three influenza viruses, which are chosen based on information about recently circulating seasonal viruses. The composition of the 2010-11 seasonal influenza vaccine will likely contain three different vaccine viruses, although committee members may consider other options. The Southern Hemisphere's 2010-11 vaccine includes the following: an A/California/7/2009 (H1N1)-like virus, an A/Perth/16/2009 (H3N2)-like virus and a B/Brisbane/60/2008-like virus. The H1 strain included in this vaccine is the same as the one used in the pandemic 2009 H1N1 vaccine.

When will the vaccine viruses selected for the 2010-11 seasonal influenza vaccine be announced?

After the FDA advisory committee meets in February to review the WHO's recommendations as they relate to the United States, the WHO and the FDA will post their recommendations for the composition of the U.S. seasonal flu vaccine on their Web sites. This information will also be available at