There are two primary types of flu virus that circulate each year and cause the office epidemics you’ve come to dread—Influenza A and Influenza B. Experts and flu shot creators have come up with a variety of options to help the public avoid both types of the flu.
The two primary umbrellas under which those options fall are trivalent and quadrivalent vaccines. Trivalent flu vaccine protects against three strains of the flu—the two Influenza A strains predicted to circulate most and the one Influenza B strain predicted to circulate most.
Quadrivalent vaccine protects against four strains of the flu—the two Influenza A strains predicted to circulate most and the two Influenza B strains predicted to circulate most. Essentially quadrivalent flu shots offer the same coverage as trivalent plus coverage against one more strain of Influenza B. Obviously that’s a bit wider coverage, and therefore a bit better protection.