Can the Flu Shot Make You Sick? Here’s the Truth, According to an Infectious Disease Doctor

There are side effects—but the flu vaccine doesn’t actually give you the flu.

can the flu shot make you sick
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Everyone’s least-favorite time of year is well on its way: flu season. Preparation can include stocking up on hand sanitizer, soft tissues, and making an appointment for your annual flu shot.

But getting vaccinated isn’t on everyone’s to-do list, in part because many people think the flu shot gives you the flu. In fact, Orlando Health Arnold Palmer Hospital surveyed 700 parents last year and found more than half of them believed the flu shot could make you sick.

So we spoke to Lisa Maragakis, MD, MPH, senior director of infection prevention at Johns Hopkins Health System and associate professor of medicine for Johns Hopkins University School of Medicine, to settle the debate once and for all.

Can the flu shot make you sick?

According to Dr. Maragakis — and the CDC, and every other flu expert on the planet — the answer is flat-out no. “It’s not a live virus vaccine,” says Dr. Maragakis. “It’s a killed or inactivated virus and can’t make you sick.”

So, why do people think the flu shot can make you sick?

The truth is, side effects of the flu shot might make you feel a little bit under the weather. “When you get a vaccine, it’s really triggering your immune system to respond so that it learns how to fight off the influenza virus and can protect you,” says Dr. Maragakis.

That process of activating the immune system can sometimes feel like you’re catching something because you start to feel achy, and your arm might get a little sore. Some people even develop a low-grade fever as the immune system responds to the vaccination—but it’s not a contraction of the flu, she explains.

Plus, there are so many different viruses circulating during the flu season, there’s no guarantee you won’t get sick from something other than the flu. “A fair number of people get the flu vaccine, and it just so happens that they caught something else around the time and they link the two things together in their minds,” says Dr. Maragakis. That’s why you also need to be cautious about washing your hands frequently and avoiding touching your face, even after you’ve had the flu vaccine.

Then there’s the chance you could catch the flu before your vaccine has had enough time to build up the antibodies that fend off influenza. That takes about two weeks, and unfortunately, it’s possible that you could catch the flu during that 14-day period. That’s part of the reason why the CDC recommends getting your flu shot before the end of October.

How effective is the flu shot, anyway?

You’ve probably heard that the flu shot isn’t 100 percent effective, and that’s true. The flu vaccine changes every year based on the specific viruses currently circling the globe. More than 100 national influenza centers worldwide retrieve flu samples from patients year-round, and based on the data they collect, they select the viruses they believe are most likely to circulate during the following flu season. In the end, the flu shot usually ends up being 40 to 60 percent effective, according to the CDC.

Why it’s still important to get a flu shot

Even if you wind up catching a flu strain that wasn’t covered in the vaccine, CDC research shows being inoculated lessens your risk of developing severe complications from the disease. And yes, flu complications can be serious. From October 2018 to early May 2019, up to 657,000 people were hospitalized with the flu, and up to 61,200 people died, according to preliminary estimates from the CDC.

It’s also important to remember that skipping the flu shot isn’t just dangerous for you — it’s dangerous for the people around you who are particularly prone to complications, such as people 65 and older, children younger than 5, pregnant women, and people with long-term medical conditions like heart disease, lung disease, and diabetes.

Not sure where to go? Here’s where you can get the flu shot all season long.

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