When does flu season start and end? 2026–27 timeline

When does flu season end?

Flu season in the United States generally winds down by late spring, around April or May, when flu activity decreases and fewer people get sick. The season runs roughly from October to May, but flu viruses can still circulate at low levels outside the typical season, so keep watching for symptoms.

CDC tracks flu activity week by week, and its reports for a season often continue well past the last busy weeks. For 2025-26, CDC was still reporting data through the week ending September 26, 2026, even though activity had dropped to low levels.

The 2025-26 flu season officially ended on October 3, 2026, and flu activity was low in early October 2026. The official end date and the end of widespread illness are not the same thing.

When does flu season start?

In the United States, flu season usually starts in the fall, around October. Influenza viruses begin spreading more widely through communities at this time, because cooler temperatures and more time spent indoors help the virus pass from person to person. The exact start date can shift slightly each year, depending on the flu strains circulating and other environmental factors.

When is peak flu season?

Flu activity usually peaks between December and February. During these months, hospitals and clinics often see a surge in flu-related visits. This is when the flu virus is most contagious and can spread rapidly through communities.

3 factors influencing the flu season duration

1. Climate and geography

Flu season timing varies by region. In colder northern states, flu season tends to start earlier and last longer. Warmer southern states may see a shorter flu season, sometimes with multiple smaller peaks. Humidity and temperature changes also affect how easily the virus spreads.

2. Virus strains and mutations

Each year, different flu strains dominate, and some are more contagious or severe than others. The flu virus constantly changes through mutations, which can influence how quickly it spreads and how long the season lasts. This is why annual flu vaccines are updated to match the most common strains.

3. Human behavior and public health measures

Changes in social behavior, like increased travel or gatherings during holidays, can accelerate flu spread. Public health efforts such as vaccination campaigns and hygiene practices help reduce transmission. The COVID-19 pandemic showed how measures like mask-wearing and social distancing can shape flu season dynamics.

Flu season: what to do if you get sick

Recognize when to seek care

If you experience severe symptoms such as difficulty breathing, chest pain, persistent high fever, or confusion, seek emergency care immediately. For milder symptoms, telehealth services like Doctronic can provide guidance and treatment options.

Follow treatment recommendations

Your doctor may recommend antiviral medications that can shorten the flu’s duration if started early. Rest, fluids, and over-the-counter remedies also help manage symptoms.

Prevent spreading the flu

Stay home from work or school while contagious, usually at least 24 hours after fever subsides. Staying put keeps the virus away from coworkers, classmates, and people at higher risk of complications. Cover coughs and sneezes, and clean commonly touched surfaces regularly. These habits help most during the winter peak, when flu spreads rapidly through communities. Getting vaccinated adds another layer of protection for the people around you.

How last season (2025-26) played out

CDC rated 2025-26 as moderate overall, with high severity for children. H3N2 subclade K (a newer branch of the H3N2 flu A virus) drove most of it. CDC first identified this subclade in August 2025, after the vaccine strains were already chosen, and it had drifted (changed) from the H3N2 virus in the vaccine. The US did not see an earlier-than-usual start, so the typical fall-to-winter timeline held.

• Hospitalizations: The cumulative rate was about 90 per 100,000 people through the week ending September 26, 2026. That reflects 31,513 lab-confirmed hospitalizations in CDC's surveillance network, which covers roughly 10% of the US population.
• Children: 195 flu-related pediatric deaths were reported to CDC for the season.
• A second wave: A late B/Victoria wave began in mid-February and continued into spring. If you had flu earlier in winter, a different flu virus may still have reached you later in the season.

When circulating viruses drift from the vaccine strains, the shot may protect less well against infection. CDC says it still helps protect against severe illness, hospitalization, and death.

When to get your flu shot for 2026-27

The flu vaccine is the most effective way to protect against influenza. September or October is the ideal time to get vaccinated, before flu activity ramps up. Adults 65 and older should avoid vaccination in July or August unless later vaccination might not be possible, since protection may fade over the season. Even if you miss this window, getting vaccinated later can still provide protection since flu season can last into spring.

All 2026-27 US flu vaccines are trivalent, meaning they protect against three viruses: H1N1, H3N2, and B/Victoria. All three components were updated, including a new H3N2 component that targets subclade K (J.2.4.1), the strain that drove the 2025-26 season.

For timing by age and situation, see our guide to the best time to get a flu shot in 2026.

Recognize flu symptoms quickly

Common flu symptoms include fever, cough, sore throat, body aches, fatigue, and chills. If you have these, especially during flu season, seek medical advice promptly. Early treatment can reduce the severity and duration of illness.

If you get sick: treatment within 48 hours

Antiviral medicine works best when you start it within 48 hours of your first symptoms. Early treatment can shorten fever and illness, and it may lower the risk of complications such as pneumonia (a lung infection). You do not need to wait for a positive flu test to begin treatment.

If you are at higher risk, treatment is still recommended after 48 hours. This applies to:

• People who are hospitalized with suspected or confirmed flu
• People with breathing illness that is severe or getting worse
• People at higher risk of flu complications, who should seek care promptly for any flu-like symptoms

Prescription options include oseltamivir, zanamivir, peramivir, and baloxavir. Which one fits depends on your age, health conditions, and any contraindications (reasons a medicine is not safe for you).

Doctronic's medical AI chat can assess your symptoms. If an antiviral like oseltamivir (Tamiflu) fits, a licensed doctor can prescribe one in a $39 video visit from home. Spotting flu symptoms early, such as fever, cough, and body aches, helps you start treatment inside the 48-hour window. Our guide to early flu symptoms lists the warning signs to watch for.

The Bottom Line

Flu season in the United States generally winds down by late spring, around April or May. Get your flu shot in September or October, and if symptoms start, ask Doctronic so treatment can begin inside 48 hours. Severe signs like trouble breathing or confusion need emergency care right away.