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  • Influenza
  • Vaccine Recommendations

Some of my patients refuse influenza vaccination because they insist they “got the flu” after receiving the injectable vaccine in the past. What can I tell them?

There are several reasons why this misconception persists:

  • Fewer than 1% of people who are vaccinated with the injectable vaccine develop flu-like symptoms, such as mild fever and muscle aches, after vaccination. These side effects are not the same as having influenza, but people confuse the symptoms.
  • Protective immunity doesn’t develop until 1–2 weeks after vaccination. Some people who get vaccinated later in the season (December or later) may be infected with influenza virus shortly afterward. These late vaccinees develop influenza because they were exposed to someone with the virus before they became immune. It is not the result of the vaccination.
  • For many people, “the flu” is any illness with fever, cold symptoms or gastrointestinal symptoms. If they get any viral illness, they may blame it on flu vaccine or think they got “the flu” despite being vaccinated. Influenza vaccine only protects against certain influenza viruses, not all viruses.
  • Influenza vaccination is our best protection against influenza disease; however, some people who are vaccinated will still get influenza illness despite vaccination.

While vaccine effectiveness (VE) can vary, recent studies show that influenza vaccination reduces the risk of illness by between 40% and 60% among the overall population during seasons when most circulating influenza viruses are well-matched to the vaccine. VE is generally lower for adults age 65 years and older. Influenza vaccination has also been shown to reduce influenza disease severity even if someone does get sick after vaccination, and reduces the risk of influenza hospitalization, and deaths in children and adults. Influenza vaccination also reduces the risk of acute cardiac events, like heart attack and heart failure, among people with heart disease.

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Last reviewed: September 10, 2023

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