quadrivalent (four virus) flu vaccines are expected to be at least as effective as trivalent (three virus) vaccines since both flu vaccines protect against three of the same influenza viruses. if an influenza b virus that is different from the trivalent vaccine influenza b component circulates the quadrivalent flu vaccine might provide better protection than trivalent flu vaccines by protecting against this additional influenza b virus. cdc evaluates the effectiveness of available flu vaccines throughout the flu season but the quantity and quality of data necessary to compare the effectiveness of different types of flu vaccine usually aren’t available until after the flu season is over and even then can be limited by what vaccine options people purchase or use during the season.
is quadrivalent vaccine more effective than trivalent?