July 27, 2022

Can the Flu Shot Give You the Flu?

The vaccine is a safe, effective way to prevent influenza — and it won’t give you the virus

Person is getting a flu shot at a clinic by a nurse.

Let’s get right to the point: A flu shot CANNOT give you the flu. Claims to the contrary are nothing more than myths.

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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?

The answer is no. Flu vaccines given through a shot in the arm are made with either inactivated (or killed) viruses or with only a single protein from the flu virus, according to the Centers for Disease Control and Prevention (CDC).

Neither the inactivated virus nor the single protein will cause the flu, according to the CDC.

“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 includes a live influenza virus that has been weakened so that it won’t cause an illness, reports the CDC.

Use of the nasal spray is more limited that the traditional flu shot. The spray vaccine is approved for healthy, non-pregnant people aged 2 to 49. People with weakened immune systems or chronic conditions (heart, lung or kidney disease) shouldn’t get the nasal spray flu vaccine.

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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, after all, is really just a way of tricking your body into thinking it has the flu. That causes it to make the antibodies that will eventually protect you if you’re exposed to the virus, explains Dr. Englund.

“So actually, a few side effects can be a good thing,” she says. “It’s a sign your body is doing exactly what it should be doing.”

And the really good news? Flu shot symptoms — including soreness at the site of the shot — typically disappear within 24 hours to 48 hours. “That’s a lot less than what you’d be dealing with if you really got influenza,” notes Dr. Englund.

Can the flu vaccine cause an allergic reaction?

A severe allergic reaction to a flu shot is extremely rare. A 2016 study found between 1.35 and 1.83 cases of anaphylaxis (an allergy to the shot) per million influenza vaccines delivered.

Does the flu shot really work?

A flu shot definitely offers a layer of protection against the virus. Annual CDC studies typically show the flu vaccine to be between 40% and 60% effective at keeping influenza infections at bay.

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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.

“Influenza vaccines have been around for many, many decades and are exceptionally safe,” reassures Dr. Englund. “We know that they save lives. So, it’s tremendously important to get your flu shot to protect yourself and those around you.”

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