TABLE 1.

Influenza virus strains in the yearly inactivated influenza vaccine^a

^aThe influenza A H1N1 virus strains in light red represent antigenically similar drifted variants; the A/California/4/2009 strain (dark red) was an antigenically novel shifted H1N1 strain. The influenza A H3N2 virus strains have remained relatively similar with only minor variations due to drift since the 2006-2007 season. For the influenza B virus, the Victoria (Vic) or Yamagata (Yam) lineage is indicated in parentheses.