Can I get influenza from the influenza vaccine?

The influenza vaccine cannot cause influenza (the flu) if you're vaccinated with the inactivated trivalent vaccine, made with killed virus. However, fever and achiness can occur after a flu vaccine. This is not the flu, however, but the result of an activated immune system.

The nasal flu vaccine, which contains a weakened live virus, could, conceivably, cause the flu in someone with a suppressed immune system. Thus, it is only approved for use in healthy people between ages 2 and 49 (younger and older people tend to have weaker immune systems). Studies involving hundreds of healthy children and adults showed no evidence that the nasal flu vaccine resulted in the flu.

However, you can get the flu after being vaccinated if the viral types used to make the vaccine do not match the circulating flu viruses. These viruses change every year, which is why the vaccine changes every year and why you need an annual vaccine. Nonetheless, in any given year the flu vaccine typically protects about 60% of healthy adults under 65. The older you are, the less effective it is, likely because of a weaker immune system.

Even when the vaccine and viruses aren't well matched, the vaccine still protects a considerable number of people. Plus, if you get the flu, having had a vaccine can mean a quicker recovery with fewer complications. And don't forget it takes about two weeks after you're vaccinated before the vaccine fully engages your immune system. During those two weeks, you're still susceptible to an influenza virus, even one the vaccine should protect against.

Check out Dr. Know's explanation about flu shots, which can't really give you the flu. Learn more about influenza in this video from Discovery.

Stacy Wiegman, PharmD
Pharmacy Specialist
You cannot get influenza (the flu) from the influenza vaccine. Viruses used in the vaccines are either dead or extremely weakened. Some of the side effects of influenza vaccines resemble those of influenza. However, these are not an indication that you have the flu.

Dr. Diana K. Blythe, MD

Flu shots do not give you the flu, or influenza. What flu shots do is train your body to attack the flu. When your body is shown the flu shot, it creates an immune response which is like your body training for fighting off the flu. You may get a slight elevation in temperature and some pain at the site of injection, but it does not give you the flu.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.