Can You Get the Flu From a Flu Shot?

Many people worry about getting a flu shot because they are afraid they will get the flu from the vaccine. There are so many stories out there about people that supposedly came down with the flu a few days after getting the shot.

But contrary to popular belief, it is not possible to get the flu from the flu shot. To put it in technical terms, correlation does not equal causation. Meaning, just because you got the flu (or more likely, another viral illness) soon after getting the vaccine, that doesn't mean the vaccine caused it. 

The injected flu vaccine (the flu shot) is actually made from a killed virus (meaning it is not infectious) and the nasal flu vaccine (nasal spray) is made from a single gene from a weakened live virus.

Neither of these vaccines can give a healthy person the flu; rather they help the body to produce an immune response without contracting an infection.

What to Expect From a Flu Shot

Possible side effects from the injected flu vaccine include:

  • Soreness, redness or pain at the injection site
  • Low-grade fever
  • Body aches

These side effects usually occur soon after the vaccine is administered and last one to two days. On very rare occasions, a severe or life-threatening reaction called Guillain-Barré syndrome may occur. However, even this has not been definitively linked to the vaccine.

What to Expect From the Nasal Flu Vaccine

The CDC's Advisory Committee on Immunization Practices has recommended that the Live Attenuated Influenza Vaccine (LAIV), commonly known as FluMist, not be used during the 2017 to 2018 flu season due to concerns about low effectiveness during previous flu seasons. Although it is still an approved vaccine, it is unlikely to be available in most places due to this recommendation. 

Possible Side Effects From the Nasal Vaccine

  • Runny nose
  • Sore throat
  • Headache
  • Cough
  • Nausea and vomiting (in children)
  • Fever (in children)
  • Muscle aches

Because the nasal flu vaccine is a weakened live virus, people in close contact with people who have severely weakened immune systems should not get the nasal flu vaccine.

Why You May Feel Sick After Getting the Flu Vaccine

First off, it's important to understand that the flu shot only protects you from influenza—not other conditions like the common cold, respiratory syncytial virus (RSV) and other viruses that may cause flu-like symptoms.

But because the flu shot does cause your body to produce an immune response, you may experience symptoms similar to those caused by the flu, though they will likely be much milder and clear up after a short while. These symptoms can include redness, swelling, or pain at the injection site, as well as fever, aches and fatigue.

The vaccine also can take up to two weeks to become effective after you receive it, so if you do actually come down with the flu, it's likely that you were already exposed to the virus before receiving your shot.

Finally, the flu shot also varies from year to year because scientists work to target the strains that research suggests will be the most prevalent that season. Despite their best efforts, they may sometimes get it wrong and not match it exactly to all circulating strains. Still, research has consistently shown that those vaccinated against the flu are far less likely to become infected than those who don't.

A Word From Verywell

Very rarely, a person may experience a true significant side effect or reaction from a vaccine. This can occur as a result of any vaccine—not just a flu shot. If you are concerned that you may have had a true injury from a flu shot, you can report it to the National Vaccine Injury Compensation Program. You should also talk to your healthcare provider so she can help you decide whether the vaccine is likely at fault or if your symptoms could be related to something else. 

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Article Sources

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  1. Centers for Disease Control and Prevention. How well flu vaccines work.

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