Flu vaccine remains effective throughout season, experts say

Health experts advise that getting a flu vaccine is beneficial at almost any point during the flu season, which typically runs from October through May in most U.S. regions. While the optimal time for vaccination is before the season starts—usually in September or October—receiving the shot later, even in January or early spring, still offers protection while the virus circulates in the community.

The vaccine takes about two weeks for the immune system to develop full protection, so planning ahead of peak flu activity, which often occurs between December and February, is recommended. Early vaccination in July or August may be appropriate for young children needing two doses or for pregnant individuals close to delivery, but overall effectiveness can wane if administered too far in advance.

Studies indicate that flu vaccine protection generally lasts at least six months, though it diminishes over time, underscoring the need for annual vaccination. Even those who have already contracted the flu are encouraged to get vaccinated, as the shot targets multiple strains and does not protect against a single strain already encountered.

Flu shots are widely available at doctors' offices, pharmacies, drive-through clinics, community centers, hospitals, and local health departments. The vaccine is safe for most people, including those with egg allergies, but is not recommended for individuals with severe allergic reactions to the vaccine, infants under six months, or those with a history of Guillain-Barré syndrome without medical consultation. Minor illness on the day of vaccination may not preclude receiving the shot, though a healthcare professional should be consulted.

Common mild side effects include low-grade fever, headache, muscle aches, and fatigue, reflecting the immune response rather than flu infection. After vaccination, individuals may wish to avoid strenuous arm exercise and limit alcohol intake for a short period to reduce discomfort.