The Center for Disease Control (CDC) encourages people to get vaccinated throughout the flu season, which can begin as early as October and last as late as May. For a typical flu season, vaccination should begin in mid-October, assuring strong immunity throughout the season.
Vaccination before December is best since this timing ensures that protective antibodies are in place before flu activity is typically at its highest. Over the course of the flu season, many different influenza viruses can circulate at different times and in different places. As long as flu viruses are still spreading in the community, vaccination can provide protective benefit.
In addition, there are other people who may benefit from seasonal flu vaccination as late as April or May, even if influenza viruses are no longer circulating in the United States. This includes:
- Persons likely to be traveling to the Southern Hemisphere where influenza may be circulating and
- Children younger than 9 being vaccinated for the first time who still have not received their second recommended dose of vaccine. Studies have shown that two doses are needed in children younger than 9 the first year they are vaccinated in order to maximize the protective benefit from vaccination.