Flu season is approaching, and federal health officials say most people should get vaccinated in September or October, ideally by the end of the month. That guidance applies to everyone 6 months and older, with rare exceptions, according to the Centers for Disease Control and Prevention.
Doctors are pushing that timeline for a practical reason. Flu usually spreads in the United States between October and May, and the vaccine takes about two weeks to provide protection, according to the CDC and the American Medical Association.
Federal guidance sets an end-of-October target
The CDC says everyone 6 months and older should get a flu vaccine every season, except in rare cases. For most people who need one dose, the agency says September and October are generally good times to get vaccinated, and that people should ideally be vaccinated by the end of October.
That message is also reflected in the CDC’s clinical guidance for providers. The agency says vaccination should ideally be offered during September or October, but it should continue after October and throughout the flu season as long as influenza viruses are circulating and vaccine remains available.
The CDC also says most adults, especially people 65 and older and pregnant women in the first or second trimester, generally should not get vaccinated too early in July or August because protection may decrease over time. Pregnant people and people with certain chronic health conditions are among those the agency specifically says should get a flu shot.
Physicians have been using a simple calendar marker to get the point across. In a recent American Medical Association article, Dr. William Schaffner said people can get the vaccine before late fall, but should time it for September or October because protection takes about two weeks to develop. His advice was direct: “Get it done by Halloween.”
That shorthand lines up with broader pediatric guidance as well. The American Academy of Pediatrics says children 6 months through 8 years old who are getting influenza vaccine for the first time, who have received only 1 dose before July 1, 2026, or whose vaccination status is unknown should be offered vaccination as soon as vaccine becomes available. They should get 2 doses at least four weeks apart, ideally by the end of October.
The AAP says the same timing matters for children who need those two doses because they need enough time to complete the series before flu activity builds. The group also says influenza vaccine can be given at the same visit as a COVID-19 vaccine, or at any time before or after it.
Even with the October target, health officials say missing that window does not mean the chance to benefit is gone. The CDC says vaccination should continue after October and throughout the season while flu viruses are circulating. Its public guidance also says getting vaccinated in December or later can still be protective.
The CDC’s vaccine information statement says flu is a contagious disease that spreads around the United States every year, usually between October and May. That is why doctors are pressing patients to plan ahead now, before cases rise and before holiday schedules make routine care harder to fit in.
The stakes are not small. The AMA, citing preliminary CDC data, said the 2025-2026 flu season caused at least 32 million illnesses, 390,000 hospitalizations and 24,000 deaths in the United States. In the prior 2024-2025 season, the AMA said CDC estimated flu vaccination prevented about 10 million illnesses, 5 million medical visits, 185,000 hospitalizations and 12,000 deaths.