Side Effects Of The Flu Shot Explained

Getting your annual flu shot is a great way to help protect yourself against the flu virus. In fact, the flu vaccine prevents millions of infections and thousands of the hospitalizations and deaths in the United States every year (via Insider). While the flu shot isn't 100% effective, it can reduce your chances of getting the flu and becoming severely ill by up to 60%. That's because the flu shot works by introducing a dead or inactivated version of the flu virus into your body, which prompts your immune system to produce antibodies to help fight off the infection.

"So, if you've had the flu shot and get coughed on by someone who has the flu, your immune system has already seen the flu and has practiced killing it," Dr. Emily Temple-Wood, a family medicine resident at Lutheran General Hospital, told Healthline. "That means that if you get sick at all, it'll be less severe." This immune response, however, can often cause some mild and temporary side effects. The most common side effect of the flu vaccine is pain, redness, and swelling near the injection site, which is usually on the upper arm.

Can you get the flu from the flu shot?

Despite the longstanding myth, you can't get the flu from the flu shot. Since the flu shot is an inactivated version of the virus, there's no way that you could actually contract the flu from the vaccine (via Health). However, it's not uncommon for some people to experience mild flu-like symptoms a few hours after getting the vaccine. Body aches, headaches, muscle pain, fever, and nausea are all common side effects of the flu shot that also resemble symptoms of the flu virus.

Of course, these side effects are much more mild and short-lived than they would be if you actually had the flu. These symptoms usually resolve on their own with 24 to 48 hours after getting the vaccine. If they do last longer, however, you should contact your doctor. Since it takes a full two weeks to be considered fully protected against the virus, you might have contracted the flu shortly before you were vaccinated.