Can the Flu Shot Make You Sick? We Asked the Experts

With a potential tripledemic on the way, it's important to protect yourself and your immune system from serious infection. One way to do that: getting your flu shot. According to the Centers For Disease Control and Prevention (CDC), only one in two Americans got a flu vaccine in the 2021-22 flu season. But adults who were vaccinated against the flu were 43 percent less likely to be hospitalized because of flu illness or related complications, the CDC reports.

One of the most common reasons people put off getting their flu shot — or worse, skip it altogether — is because they think the flu shot will make them sick or even cause them to become infected with the flu itself. But that's a misconception. 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. That being said, while you can't get the flu from the flu shot, it is possible to get sick with something else around the time of your shot.

"People can also get sick from other viruses around the time when they get the flu shot," Michael Ison, MD, a professor of infectious diseases at Northwestern University Feinberg School of Medicine and a practicing physician at Northwestern Medicine, tells POPSUGAR. "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 doesn't guarantee protection from the disease. "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," says Carolyn Kaloostian, MD, MPH, a clinical assistant professor of family medicine at the University of Southern California Keck School of Medicine. Still, better safe than sorry — and if you do feel sick after your flu vaccine, here's what you need to know.

Why You Feel Sick After the Flu Shot

In the United States, flu vaccines are designed to protect against the four most common flu types anticipated in the upcoming flu season, per the CDC, which is why they're called "quadrivalent vaccines." The flu shot works by introducing inactivated (killed) flu viruses to the body, which prompts your immune system to make antibodies. The antibodies — which develop after your shot — are specifically created to learn how to recognize the flu virus and kill it, meaning if you're exposed to the flu, you're much less likely to get sick.

The flu shot does not give you the flu, but there are some common side effects. "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," Dr. Ison says.

It takes roughly two to three weeks for those antibodies to form, Dr. Kaloostian explains. 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.

In short, the flu shot protects you from getting sick by activating your immune system and developing antibodies. Sometimes, you may experience side effects as a result — but it means the vaccine (and your body!) is doing its job.

Flu Shot Side Effects

According to the CDC, flu shot side effects are usually very mild and go away on their own within a few days. Side effects may include:

  • Soreness
  • Redness or swelling at the site of the shot
  • Low-grade headache
  • Fever
  • Nausea
  • Muscle ache
  • Fatigue
  • Like with any injections, the flu shot can sometimes cause fainting.

The CDC reports that severe reactions to the flu shot are very rare. However, if you experience breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness, these are all signs of a serious allergic reaction. You should call your doctor immediately and seek medical attention.

Treating Flu Shot Side Effects

If you are experiencing mild side effects from your flu shot, there are several at-home treatment methods to help with the discomfort. Remember, you're allowed to baby yourself a little — or take off work if you need to. For headache, arm pain or tenderness, and mild fever, the Cleveland Clinic recommends taking an over-the-counter pain reliever and fever reducers like Tylenol or Advil. If you're feeling nausea or dizziness, rest, drink plenty of fluids, and consider clear or ice-cold drinks, per the Cleveland Clinic. And if you're feeling really sick after a flu shot, it's never a bad idea to check in with your healthcare provider.

This information in this article is not medical advice. You should always consult your doctor regarding matters pertaining to your health and before starting any course of medical treatment.

— Additional reporting by Sara Youngblood Gregory and Alexis Jones