In the U.S. the months of September and October are recommended as the best months to be vaccinated if you only need one dose of a flu vaccine. It takes about 2 weeks after a flu vaccine to build immunity against the virus.

Children who are 6 months through 8 years of age who require two doses (usually because it’s the first season they are vaccinated) should receive the first dose as soon as the flu vaccine is available.

Annual vaccination during July and August is not recommended for most people, especially adults (particularly those aged ≥65 years) and pregnant persons in the first or second trimester (unless there is concern that later vaccination might not be possible).

However, vaccination during July and August can be considered for children of any age who require only 1 dose and for pregnant persons who are in their third trimester during those months.

If you or your child does not get the flu vaccine in September or October, you should still talk to your doctor or pharmacist about getting a flu vaccine. Vaccination is continued throughout the season if flu viruses are still circulating.