Flu Vaccine Effectiveness Variability

Annual flu vaccines demonstrate effectiveness ranging from 10% to 60%, hinging on the match between circulating strains and the vaccine composition. For example, during the 2019-2020 season in the U.S., vaccination prevented an estimated 105,000 hospitalizations. Unlike the fixed protection of the HPV vaccine, flu vaccines require annual updates because the virus mutates rapidly, with two subtypes circulating each season—a challenge that experts say still justifies widespread immunization to protect vulnerable populations.