The Vaccines

In general, seasonal influenza vaccines are trivalent, containing a mixture of influenza A and B strains thought most likely to circulate in the coming season. However, monovalent vaccines have been produced against candidate pandemic strains. It is now common practice to use reassortant strains for production that give high yields of the appropriate surface antigens. Reassortant strains for vaccine production have the surface glycoproteins (HA and NA) of the circulating epidemic virus but the internal proteins of a standardized production strain, eliminating much of the risks associated with handling pathogenic strains. The virus is grown in chick embryos or cell cultures for the production of vaccines.