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Can the Flu Shot Make You Sick?

You Can Get Sick After Having Your Flu Shot, but Not For the Reasons You Think

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One of the most common reasons people put off getting their flu shot — or worse, skip it altogether — is also a misconception: that the flu shot will make you sick or even cause you to become infected with the flu virus itself. Doctors universally agree that neither is true and that getting the flu shot is your best bet for protecting yourself and your loved ones during flu season.

"The flu shot can't give you an infection; it is digested virus so there is nothing to make you sick," Michael Ison, MD, a professor of infectious diseases at Northwestern University Feinberg School of Medicine and a practicing physician at Northwestern Medicine, told POPSUGAR. "Some people will get a low-grade fever or some achiness in the day or so following vaccination. These are all signs of your body responding to the vaccine and making antibodies."

It takes roughly two to three weeks for those antibodies to form, explained Carolyn Kaloostian, MD, MPH, a clinical assistant professor of family medicine at the University of California Keck School of Medicine. If someone gets sick after being vaccinated, it's likely they were exposed to the influenza virus before the vaccine had taken effect or their body didn't develop a sufficient antibody response, which can occur with any vaccination, according to Dr. Kaloostian.

"People can also get sick from other viruses around the time when they get the flu shot," Dr. Ison said. "Cold viruses are very common in the Fall and early Winter when people get vaccinated, and you can always get sick from non-influenza infections."

It's also important to remember that, while the flu vaccine is very effective, it isn't foolproof. "The flu vaccine developed each year is the best estimate for the flu strains that are around, and if you were exposed to a different strain, you would not be protected," Dr. Kaloostian said. Still, better safe than sorry.

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