Cold, Flu, COVID & Allergy: This Season’s Guide
Flu season in the U.S. typically starts in October, peaks between December and February, and can stretch into May. The CDC recommends vaccination by the end of October because immunity takes about two weeks to develop — and because last season demonstrated how fast an early H3N2 wave can move once schools fill and windows close. [1]
This hub is the season’s home base: what’s circulating, how to tell the look-alike illnesses apart, what treats each one, and when the calendar itself is the diagnostic clue. Every page below is updated for the 2026–27 season.
When is flu season? The season at a glance
| Month | What’s usually happening |
|---|---|
| September–October | Flu activity low but building; prime vaccination window; ragweed allergy peaks until first frost |
| November | Cases climbing; first school and workplace clusters |
| December–February | Flu peak, RSV peak, winter COVID wave typically layered on top |
| March–April | Flu A fades; flu B’s late-season turn; tree pollen arrives — sick-vs-allergic confusion returns |
| May | Season’s tail; lingering B cases |
So when does flu season end? Most years, activity falls to baseline by May. Two calendar quirks worth knowing before then. The fall overlap — ragweed allergies running into early flu season — produces the year’s most misread symptoms; the cold-or-allergies check settles it in a minute. And the late-season flip: a second flu in March after a December bout is usually flu B following flu A — one doesn’t immunize you against the other.
What’s circulating this year
Flu: Last season was dominated by H3N2 viruses in the group scientists call subclade K — 88% of influenza A samples were H3N2, and 93% of those were subclade K, a variant that emerged in late 2025 and spread globally within months. This year’s vaccines were updated on all three components, with the H3N2 strain specifically chosen to cover it. [1][2] H3N2-led seasons historically run harsher for adults 65+ — more hospitalizations, more complications — which makes both the timing advice and the senior-formulation advice below worth taking literally.
COVID: The XFG (“Stratus”) family is currently dominant, with NB.1.8.1 (“Nimbus”) alongside; both spread easily but aren’t associated with more severe disease. The 2026 profile opens cold-like — a notably harsh sore throat leads, and loss of taste or smell has become rare. Full picture: this season’s COVID symptoms, and the isolation math at how long you’re contagious.
Allergies: Ragweed runs late August to first frost; indoor allergens (dust mites, pet dander, mold) take over once heating season closes the windows. If your “cold” is into week two with itchy eyes and no fever, it was never a cold.
When to get your flu shot: the practical version
- Timing: September–October is the sweet spot — protection in place before the December peak, still strong through the tail. Vaccinating in November or later still beats skipping; the season runs long.
- 65 and older: ask specifically for the high-dose or adjuvanted senior flu vaccines — they exist because standard doses under-perform in older immune systems, and an H3N2 year is exactly when that margin matters.
- Combining shots: flu shot and updated COVID booster in one visit (different arms) is standard, safe, and the most realistic way busy people actually get both done.
- Kids: everyone 6 months and up is recommended for flu vaccination; first-time vaccinees under 9 need two doses a month apart — start early enough to fit both in. [3]
- Cost: flu shots are free with virtually all insurance and Medicare Part B; pharmacies handle most of it walk-in.
Figure out what you have
- Cold vs flu: how to tell in the first 48 hours — onset speed is the tell, and the 48-hour antiviral window is the reason to care
- Flu A vs flu B: what’s the difference? — including what “subclade K” means for this year
- Is it a cold or allergies? — the 60-second check
- COVID symptoms right now — what the current variant actually feels like
- Sinus infection vs cold — the 10-day rule and “double worsening”
Treat it and stop spreading it
- How long are you contagious with COVID? — day-by-day, plus the current return-to-life rules
- Zyrtec vs Claritin: which should you take? — and when a nasal spray beats both
- How to stop post nasal drip — the four causes and the fix for each
- Paxlovid coupon & copay support — if COVID treatment enters the picture, the cost help that exists
The short version of the whole season: vaccinate by Halloween, keep a combo test in the cabinet, respect the 48-hour flu-antiviral and 5-day Paxlovid windows if you’re high-risk, and when a “cold” behaves strangely — too long, too itchy, too sudden, or better-then-worse — one of the pages above will name it.
Frequently Asked Questions
When does flu season start in the US?
Flu activity typically begins rising in October, peaks between December and February, and can run into May. Vaccination is recommended by the end of October, since protection takes about two weeks to build.
What flu strain is expected this season?
H3N2 viruses in the ‘subclade K’ family dominated last season, and the 2026–27 vaccines were updated on all three components specifically to cover it, alongside updated H1N1 and influenza B strains.
When should I get my flu shot?
September or October is the sweet spot — early enough to be protected before the December peak, late enough that protection holds through the season’s tail. Adults 65+ should ask for the high-dose or adjuvanted senior formulations.
Can you get the flu shot and COVID booster together?
Yes — same visit, different arms is standard practice, and studies show no meaningful loss of protection from co-administration. It’s the most practical way to enter the season covered against both.
Sources
This article is general health information, not medical advice, and isn’t a substitute for professional diagnosis or treatment — see our full medical disclaimer. Seasonal pages are refreshed each fall and when circulating strains meaningfully change; severe symptoms, trouble breathing, or high-risk conditions warrant a clinician promptly. For emergencies, call 911.