Each year in the United States, between 5%-20% of the population is infected with influenza; about 36,000 people die, and more than 200,000 people are hospitalized because of influenza complications.
Because influenza viruses are continuously changing, the strains of virus included in the influenza vaccine are reevaluated each year, and a new vaccine must be formulated for each season. The vaccine is typically made up of three viruses, including one influenza type B virus and two influenza type A virus strains, and each must be grown individually before the three are combined late in the production process. The strains are usually chosen in February, and the vaccine production and preparation process takes about six to eight months. Distribution of influenza vaccine begins as early as August and typically continues throughout November and December.
The viruses in the 2006-2007 influenza vaccine are:
- An A/New Caledonia/20/99 (H1N1)-like virus;
- An A/Wisconsin/67/2005 (H3N2)-like virus (A/Wisconsin/67/2005and A/Hiroshima/52/2005 strains); and
- AB/Malaysia/2506/2004-like virus (B/Malaysia/2506/2004 and B/Ohio/1/2005 strains)
For more information about influenza and influenza vaccine, visit www.cdc.gov/flu. TH