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Can the Flu Shot Give You the Flu?

gloved hand with syringe of flu vaccine
Arefa Cassoobhoy, MD, MPH - Blogs
By Arefa Cassoobhoy, MD, MPHBoard-certified internistOctober 29, 2018

This is such a doctor thing, but every year I get excited when the flu vaccine arrives. For me, it signals the start of the holiday season. And, I want everyone to get through the season – all the way from Halloween to Valentine’s Day and the fun in between – without getting sick.

An estimated 80,000 people died last year from the flu – the flu can be incredibly dangerous – so, it’s satisfying to me that a simple intervention like a shot or a nasal spray can prevent such a serious illness. That’s why I ask every one of my patients, “Have you gotten your flu shot?”

Sometimes I have a patient who refuses the flu vaccine. Often this is because they mistakenly believe that the vaccine will give them the flu. They or someone they know through the grapevine got a flu shot in the past and then got sick, leading them to conclude that the flu shot was to blame.

I’m not discounting their symptoms – they might indeed have had the cold or the flu – but it wasn’t from the flu vaccine. In fact, if they hadn’t gotten the vaccine, they might’ve gotten a lot sicker.

You cannot get the flu from the flu vaccine. The flu shots contain either dead flu viruses or they contain proteins from the flu virus – not the virus itself. The flu nasal spray vaccine uses flu viruses that are altered so they can’t give you the flu.

Now, the side effects of the flu vaccine could mimic a mild cold. And this is what some people might be experiencing. After the flu shot you might feel a little achy, sore at the injection site or have a low grade fever, and the flu nasal spray can be followed by a runny nose, headache, sore throat or cough. But none of this is even close to the intensity of the flu – where you suddenly get hit hard with fever, aches, chills, weakness, and cough.

There are people who get the flu even though they were vaccinated. It takes about 2 weeks after you get the shot or nasal spray for your immune system to build up antibodies to fight the influenza virus, so during that time you could get sick from the flu (that’s why you should get the vaccine early in the season!).

Also, the flu vaccine targets the 3 to 4 flu viruses that are the most likely to be common each season, and it usually works well. The CDC reports that during the 2016-2017 flu season, the vaccine prevented an estimated 5.3 million illnesses. But it is possible for you to get the flu from another flu virus that happens to be circulating in your community. And if you’re older or have a chronic medical issue that weakens your immune system you might also be more vulnerable to getting the flu.

After having the flu vaccine, if you do get the flu – it’ll be milder and shorter than if you hadn’t gotten vaccinated. There are plenty of studies that show the flu vaccine reduces the risk of flu-related complications that can lead to hospitalizations, intensive care stays, and even death.

Bottom line: The flu vaccine doesn’t cause the flu – it helps prevent it.

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About the Author
Arefa Cassoobhoy, MD, MPH

Arefa Cassoobhoy, MD, MPH is a board-certified internal medicine doctor and a WebMD Medical Editor. She is on the team that makes sure all WebMD content is medically correct, current and understandable. She sees patients at the Women’s Wellness Clinic at the Atlanta Veterans Affairs Medical Center.

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