What does a tetravalent influenza vaccine mean?

The tetravalent influenza virus split vaccine contains four influenza virus antigen components: Ahh1n1,A H3N2, B Yamagata strain (By) and B Victoria strain (Bv), while the trivalent influenza virus split vaccine contains three influenza virus antigen components: Ahh1n1,A H3N2 and B Victoria. The tetravalent influenza virus split vaccine developed by Hualan Bio contains the four influenza virus antigen components mentioned above, which can cover more influenza epidemic types and will effectively prevent and control the influenza epidemic.