What Is Influenza?
9. Why Is the Influenza Vaccine Annual?
The flu vaccine is adapted and released every year to combat new strains of the flu. Unlike other vaccines, a single flu vaccine may not protect you from the risk of infection from year after year.
This is in part due to the unique nature of the flu virus. This virus is highly adaptable, so every flu season includes one or more new strains. A flu vaccine improves your immune system to better combat the virus, but your antibody levels can decline over time.
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