Four influenza virus strains
H1N1 and H3N2 of Influenza A, and Victoria and Yamagata lineages of Influenza B are the common strains of human flu viruses. Until now, China had only three-strain vaccines on the market.
The four-strain vaccine adds protection against the Yamagata lineage of Influenza B, which as the main virus strain during the last flu season.
Two domestic companies -- Hualan and Changsheng -- are the approved vaccine producers. The vaccine may be used on adults and children aged three years and above.