All other currently available licensed seasonal influenza vaccines are trivalent, containing 3 strains -- 2 strains of type-A influenza (A/H1N1 and A/H3N2) and 1 B-lineage strain. FluMist Quadrivalent (influenza vaccine live) contains 4 strains (2 type-A strains and 2 type-B lineages) to help provide broad protection against circulating influenzas A and B.
In recent years, influenza B strains from 2 different lineages (B/Yamagata and B/Victoria) have circulated. The quadrivalent vaccine includes strains from both lineages, helping provide protection against both B lineages.
“A vaccine containing the four virus strains most likely to spread and cause illness during the influenza season offers an additional option to aid in influenza prevention efforts,” Karen Midthun, MD, director of FDA’s Center for Biologics Evaluation and Research, said in FDA’s announcement of the approval.
