Flublok Quadrivalent

Flublok Quadrivalent contains recombinant haemagglutinin (HA) proteins of the four strains of influenza virus specified by health authorities for inclusion in the annual seasonal vaccine. Using the recombinant production technology, the HA in Flublok Quadrivalent has an identical primary structure to the HA in the wild type virus strains selected for seasonal vaccines without the mutations that may occur when the virus is adapted to grow in a culture matrix that is foreign to the wild-type strain. This assures the vaccine viral strains represent antigens that are an exact match to the World Health Organization (WHO) selected strains which induce the desired humoral immune response (as measured by hemagglutination inhibiting (HI) antibody that is known to protect against influenza infection). Antibodies against one influenza virus type or subtype confer limited or no protection against another. Furthermore, antibodies to one antigenic variant of influenza virus might not protect against a new antigenic variant of the same type or subtype. Frequent development of antigenic variants through antigenic drift is the virologic basis for seasonal epidemics and the reason for the usual replacement of one or more influenza virus strains in each year's influenza vaccine. Therefore, influenza vaccines are standardised to contain the hemagglutinins of influenza virus strains (that is, typically two type A and two type B), representing the influenza viruses likely to be circulating in the upcoming season. Annual influenza vaccination is recommended because immunity during the year after vaccination declines and because circulating strains of influenza virus change from year to year.