Doctors advise optimal timing for flu vaccination to ensure protection through season
Infectious disease specialists say flu shots given too early may lose effectiveness before the season ends, recommending vaccination in October for most people.
U.S. health experts caution that receiving a flu vaccine before October can reduce its protective benefit by the time the influenza season peaks. The Centers for Disease Control and Prevention (CDC) estimates that last season caused roughly 32 million illnesses, 390,000 hospitalizations and 24,000 deaths. While the vaccine does not guarantee immunity, it lowers the risk of severe disease.
Infectious disease physicians—including William Schaffner of Vanderbilt University, Amesh Adalja of Johns Hopkins, Melinda Haas of the University at Buffalo, and Thomas Russo of the same institution—explain that flu-shot immunity typically lasts six to eight months, but wanes over time. “If one gets the flu shot too early, your protection may run out before the end of flu season,” said Dr. Russo.
The CDC notes that flu activity generally rises in October, peaks between December and February, and can linger into spring. Because it takes about two weeks for antibodies to develop after vaccination, experts recommend receiving the shot in October, ideally by Halloween, to align peak immunity with rising virus circulation. Dr. Adalja adds that “the vaccine will last further into the season if administered in October.”
Children under eight who have never been vaccinated require two doses spaced at least four weeks apart, so an early dose may be appropriate for that group. For most adults, waiting until late October balances early protection with sustained immunity. If vaccination is delayed, health officials stress that it is still beneficial to receive the shot during the season.
The CDC advises adults 65 and older to receive a quadrivalent vaccine, while younger adults typically receive a trivalent formulation. Egg-free and mRNA-based flu vaccines, as well as the nasal spray FluMist, are also available. High-risk individuals may consider additional preventive measures such as mask use, hand hygiene, and avoiding close contact with sick persons.