Can the Flu Shot Give You the Flu?

A common concern is that the flu shot might actually give you the flu. While it’s easy to see why people might think that, the science behind the vaccine shows that’s not the case.

The problem, though? While science clearly says one thing about influenza vaccines, various people in your life may offer a different opinion. So, let’s talk facts about the flu shot with infectious disease expert Kristin Englund, MD.

Does the flu shot contain an active flu virus?

Flu shots don’t contain the live virus. Instead, they use either an inactivated (killed) version of the virus or a single protein that teaches your immune system how to respond. That’s why the vaccine itself can’t cause influenza.

“You can’t get the flu from a flu vaccine,” says Dr. Englund. “I know that’s always one of the big concerns. But we’re not giving you a live virus, so you can’t get the flu from it.”

What about the nasal spray flu vaccine?

The nasal spray flu vaccine does contain a live, but weakened, virus. For most healthy people, it isn’t strong enough to cause illness. Though it isn’t recommended for those with weakened immune systems or certain health conditions like heart, lung or kidney disease.

Why do some people feel sick after getting a flu shot?

It is possible that a flu shot leaves you with flu-like symptoms. Some people may get a mild fever, a headache or feel fatigued. Consider that a sign that your body is responding to the vaccine.

The flu vaccine safely trains your immune system to recognize and fight the flu virus. That causes it to make the antibodies that will eventually protect you if you’re exposed to the virus, explains Dr. Englund.

“Some people notice mild side effects like fatigue, headache, or a low fever,” she says. "These reactions are normal and show that your immune system is building protection.“That’s a lot less than what you’d be dealing with if you really got influenza.

Can the flu vaccine cause an allergic reaction?

Like any medical treatment, the flu vaccine carries some risk. Severe allergic reactions are possible, but very rare. Research suggests only 1–2 cases per million doses.

Does the flu shot really work?

Studies show that flu shots are typically 40% to 60% effective at preventing infection. Even if you still catch the flu, vaccination can lower the risk of complications or hospitalization. For many people, that makes it a helpful extra layer of protection.

And even if you get sick from the flu, vaccination can reduce your risk of more serious complications and hospitalization.

Dr. Englund advises getting your flu shot as soon as possible to offer protection during flu season, which occurs in the fall and winter in the United States. Activity typically peaks during and after the holidays.

“Flu vaccines have been widely used for decades, and doctors generally consider them very safe," reassures Dr. England. “If you’re weighing whether to get one, talk with your healthcare provider about whether it makes sense for you this season.”