How often should adults receive a flu vaccine?

Adults should receive a flu vaccine annually, typically before the onset of flu season, to ensure optimal protection against the virus. The flu virus changes frequently, and the vaccine is updated each year to match the circulating strains. Annual vaccination helps maintain immunity at a protective level, especially as immunity from the previous year's vaccine can diminish over time.

Receiving the vaccine before flu season allows the body sufficient time to build up immunity, reducing the risk of infection when the virus is most prevalent. This strategy is particularly important for high-risk populations, including older adults and individuals with chronic health conditions, who may experience more severe complications from influenza.

The other options do not align with the recommended vaccination schedule: receiving it every six months may lead to unnecessary vaccinations without the need for such frequency, vaccination every two years does not account for the changing strains, and waiting until flu symptoms appear significantly reduces the effectiveness of the vaccine and may leave individuals unprotected during high-transmission periods.