Each year the U.S. Centers for Disease Control and Prevention (CDC) and vaccine manufacturers try to predict which strains are most likely to cause flu epidemics for the next year and then produce vaccines tailored to those strains. Because of the constant change in the flu virus, the vaccine needs to be changed each year to protect against the flu strains that are expected to be responsible for that year’s flu infections
For the 2007-2008 season, the strains are
A/Wisconsin/67/2005 (H3N2)-like virus A/Wisconsin/67/2005 or A/Hiroshima/52/2005 strains)
A/Solomon Islands/3/2006 (H1N1)-like virus
B/Malaysia/2506/2004-like virus B/Malaysia/2506/2004 or B/Ohio/1/2005 strains)
A strain is named based on its type (A, B, or C), where it was first isolated it used to be country-based, but now isolations can be localized to a particular city, the year of isolation the last two digits of the year, and also of the strain number, the A/Wisconsin strain for this year was isolated in 2005, and the serial number of the isolation for that year.