Flu viruses usually cause the
most illness during the colder months of the year. In the United States, flu season
is from October to May. Most cases happen from late December to early March.
It's best to get the flu
vaccine early in flu season, ideally by the end of October. That way, the body
has time to make antibodies that protect it from the flu.
What if you aren't vaccinated by then? Getting the vaccine later is better than
not getting it at all. It's still flu season well into spring — even then it's
not too late for you and your family to get the flu vaccine.