When Does Flu Season Start 2025 Cdc. Trivalent flu vaccines are formulated to protect against three flu viruses (an a(h1n1) virus, an a(h3n2) virus, and a b/victoria virus). If you get it too early, say in july or august, you “might run out of immunity by the.
Cdc reports showed that national flu activity. But when it comes to flu season, the cdc says flu cases typically start to rise in october and peak between december and february.