When is flu season?
Last updated September 3, 2026.
Per the CDC: flu circulates in fall and winter - activity usually starts climbing in October, peaks December to February, and can run as late as May, with timing less predictable since COVID. Two consequences. Vaccine timing: the shot takes about two weeks to full protection, so September-October is the sweet spot; but later still counts - the back half of the season is long. And the peak-month behaviors: hand washing, staying home feverish, and taking antivirals early (best within two days of symptoms) when prescribed. The firm-appointment group: 65-plus, pregnant women, anyone with asthma, diabetes, heart disease, or weakened immunity - and their households. Pymander is a free AI doctor, 24/7 by text, and can help you sort flu from a cold in season.
What to do
- Book the shot for September or October: two weeks to full effect.
- Missed it? Get it anyway: the season runs months.
- High-risk? Treat it as a firm date: and ask early about antivirals if sick.
- December to February: extra hand hygiene: that is the peak.
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