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
Common questions
When is flu season?
Flu season in the US runs on a fairly reliable clock, per the CDC's season tracking: flu viruses circulate in fall and winter; activity typically starts increasing in October, peaks most years between December and February, and can keep going as late as May - though the CDC notes timing has been less predictable since the COVID pandemic. Two practical consequences. First, the vaccine timing: the flu shot takes about two weeks to reach full protection, so September and October are the sweet spot - protected before the December-to-February peak. Missed the window? Get it anyway: late vaccination still protects through the back half of the season, and 'too late' only really means the season is over. Second, the everyday-season behaviors: the peak months are when the boring defenses pay - hand washing, staying home when feverish, and taking antivirals seriously if a doctor prescribes them early in the illness (they work best within the first two days). Who should treat flu season as a firm appointment: adults 65 and older, pregnant women, anyone with asthma, diabetes, heart disease, or a weakened immune system, and the people who live with them - the complications that make flu dangerous concentrate there. Pymander is a free AI doctor, 24/7 by text, that can help you sort flu from a cold in season.