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How well does the flu vaccine work?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Aug 10, 2023.

Official answer


Flu vaccination typically reduces the risk of flu illness by between 40% and 60% during seasons when the flu viruses are well-matched to the flu vaccine. But if you are infected with the virus, the vaccine reduces your chances of getting the flu and passing it on to others, and lessens the severity of symptoms, hospitalizations and death.

It's important to know that each year the flu vaccine is never 100% effective in preventing flu. Vaccine effectiveness varies from year to year, based on the match of the circulating flu types to the strains contained in the vaccine.

  • In 2022-2023, interim analyses indicate that influenza vaccination substantially reduced the risk for medically attended influenza among persons aged <65 years and for symptomatic influenza in children and adolescents.
  • For example, flu vaccine effectiveness estimates through Feb. 2023 show that the 2022-2023 vaccine reduced the risk of illness needing medical care by about 54% among persons 65 years age and younger with Influenza A, the most common flu virus that season.
  • In children and adolescents less than 18 years, the flu vaccine was 71% effective for preventing symptomatic influenza A illness.

All vaccines in the 2022-2023 flu season were quadrivalent, meaning they targeted 4 strains of the flu, 2 type A flu viruses (H1N1 and H3N2) and 2 type B flu viruses (Victoria and Yamagata lineage) and were well-matched to the circulating viruses. Each year, flu viruses may mutate, meaning new vaccine components will be needed.

Commonly used flu vaccines include:

Annual influenza vaccination is the best strategy for preventing influenza and its complications. Strains can change from year-to-year, and that's one reason why you need the latest flu vaccine each fall. The U.S. Centers for Disease Control (CDC) recommends that eligible persons aged 6 months and older receive a yearly flu vaccine (with rare exceptions), typically in the early fall (Sept or Oct).


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