According to the Food and Drug Administration (FDA), vaccinations can be protective as long as flu viruses are circulating. And although seasonal flu outbreaks can happen as early as October, flu activity usually peaks in January or February, and can last well into May.
Why a new vaccine?
According to Marion Gruber, Ph.D., director of FDA’s Office of Vaccine Research and Review, there are several reasons that new vaccines must be manufactured each year.
“Influenza viruses can change from year to year, due to different subtypes and strains that circulate each year,” says Gruber. A vaccine is needed that includes virus strains that most closely match those in circulation, and the protection provided by the previous year’s vaccine will diminish over time.