The flu shot will not give a person influenza, or the flu. Instead, it should help prevent the infection, which causes a significant number of visits to the doctor in the United States each year.

According to research from 2015, an estimated 43% of people in the United States believe that getting the flu vaccine can give a person the flu. However, this is a misconception.

In this article, learn about why the flu shot does not cause the flu, some reasons a person might get sick after getting a vaccine, and how the shot helps protect against illness.

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A headache is a common side effect of the flu shot.

Some people believe that the flu vaccine contains living viruses and can give a person the flu. This is not true.

Scientists make the most common flu vaccine using an egg based manufacturing process. The vaccine contains inactivated, or dead, flu viruses.

When a health professional injects the vaccine into a person's body, the person's immune system starts to develop antibodies to fight the illness — even though the virus is inactive.

If a person comes into contact with flu virus again, their body will recognize it and already has the right antibodies to attack it quickly and keep a person from getting sick.

Many other misconceptions about the flu shot causing the flu are due to the side effects a person can experience after they get the shot.

Examples of these side effects include:

  • headache
  • low-grade fever
  • muscle aches
  • tenderness, swelling, or redness at the injection site

According to the Centers for Disease Control and Prevention (CDC), these symptoms tend to appear shortly after receiving the shot and will go away within 1–2 days.

Researchers have conducted studies wherein people received either a flu shot or a shot that contained just salt and water.

The participants reported similar symptoms, including fever, cough, and runny nose, regardless of whether they received the vaccine or the placebo. The only main difference in symptoms was that those who received the flu shot reported more soreness at the injection site.

There are several reasons a person may get sick after receiving a flu shot.

Some people may think that they have the flu when they are ill due to a different viral or bacterial infection. This is because many flu symptoms are similar to those of the common cold, which can also occur during flu season.

It takes about 2 weeks for a person to develop immunity to the flu after receiving a flu shot. During this time, it is possible that a person could be exposed to the flu virus and become sick.

The flu vaccine represents researchers' best predictions about which flu virus strains will be most prevalent for that year. However, a person can still come into contact with a strain of flu virus that they are not immunized against.

The primary benefit of getting the flu shot is preventing the illness. This also helps prevent its symptoms, including high fevers, chills, a racking cough, muscle aches, and extreme fatigue.

Getting the flu shot also contributes to something called "herd immunity." Herd immunity helps prevent the overall incidence of flu, as people who get the vaccine do not get the flu and therefore cannot pass it to other people.

The CDC explain that for the 2016–2017 flu season, the flu shot:

  • prevented an estimated 5.3 million people from getting the flu
  • reduced flu-related visits to the doctor by 2.6 million
  • reduced flu-related hospitalizations by 85,000

The CDC also note that in 2012–2015, getting the flu vaccine reduced a person's likelihood of requiring admission to an intensive care unit by 82%. The shot also lowers the risk of childhood death from the flu.

The flu can be life threatening to people of all ages. Even healthy young people can die from flu complications. It is important not to underestimate the seriousness of this illness.

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Older adults may be more at risk of flu complications.

Anyone can experience flu complications. However, some people are more likely than others to experience the most severe side effects of the flu.

People at risk of complications include:

  • older adults
  • people with cardiac disease
  • people with weaker immune systems, such as those with HIV
  • pregnant women
  • people with chronic lung conditions
  • children

Even if a person does not fall into any of these categories, getting the flu vaccine helps protect those at greater risk.

Getting the flu shot will not give a person the flu. It can protect against getting the virus and spreading it to others.

Although a person may have some mild feelings of discomfort for a few days after getting a flu shot, they are usually minor symptoms. Getting the flu itself can cause symptoms that are much more severe.

Doctors usually release the flu vaccine in early fall. Ideally, a person should get the vaccine before late October.

It is never too late to get the flu shot. Even getting the flu shot in the spring can still protect a person against potential exposure.