A flu shot is a vaccine for preventing influenza. Influenza, or the flu, is a seasonal virus that affects the respiratory system. Vaccination is important for people at risk of severe illness from the flu.

Flu shots can have some mild side effects, such as pain and bruising at the injection site. However, getting the flu vaccine every year is the best option to prevent flu from spreading and causing severe illness.

In this article, we discuss the benefits and risks of flu shots.

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A person receiving a flu shot may get pain and bruising at the injection site.

Flu shots are very safe.

Over the past 50 years, several hundred million people in the United States have safely received flu vaccines. Severe reactions to flu shots are extremely rare. For every million flu shots, severe reactions occur in about 0.2 cases.

Before approving a flu shot for public use, the Food and Drug Administration (FDA) carefully evaluate its safety and effectiveness.

The FDA also ensure that all vaccines contain substances that comply with their strict Current Good Manufacturing Practice regulations.

The Centers for Disease Control and Prevention (CDC) and the FDA continuously monitor the safety of flu shots. They use the Vaccine Adverse Event Reporting System platform to identify and examine any adverse reactions to flu shots.

For more information and resources to help keep you and your loved ones healthy this flu season, visit our dedicated hub.

The flu can cause serious illness, hospitalization, and death in high risk individuals. High risk groups include:

  • older adults
  • young children
  • pregnant women
  • people with certain underlying health conditions, such as HIV, asthma, and diabetes

Flu vaccinations are vital for anyone at risk of severe complications. Other benefits of flu shots include:

  • reducing the severity of symptoms in those who do get the flu, potentially preventing the symptoms from disrupting daily life
  • lowering the risk of passing the flu onto high risk individuals
  • reducing the risk of death in people with hypertension
  • preventing tens of thousands of trips to the doctors each year

The CDC estimate that flu vaccinations between 2017 and 2018 prevented:

  • 6.16 million illnesses
  • 3.18 million medical visits
  • 90,904 hospitalizations
  • 5,747 deaths

Flu shots also allow the development of community immunity. If enough people get the vaccine, the flu is unable to spread rapidly through communities. As a result, people in high risk groups are less likely to get the flu.

Flu shots are, therefore, important for protecting others from severe illnesses.

Some possible downsides to flu shots include:

  • only about 40–60% of flu shots are effective in preventing the flu each year
  • they can take up to 2 weeks to start working
  • sometimes, they cause mild side effects, such as pain, redness, and swelling at the injection site
  • some people may experience low grade fever, headaches, and muscle aches after the shot, but these should only last 1–2 days
  • in very rare cases, Guillain-Barré syndrome can develop following a flu shot

A common worry is that the flu shot can cause a person to get the flu. However, as the vaccine contains either the inactivated virus or only part of the virus, this is not possible.

Pros and cons for babies and toddlers

Younger children are at a higher risk of severe illness from the flu. According to a study in Pediatrics, flu shots significantly reduce the risk of death from the flu in those between the ages of 5 and 12 years.

The American Academy of Pediatrics recommend that all children over 6 months of age should receive a flu shot. Most flu-related deaths occur in children without vaccinations.

A downside is that the shot might cause discomfort in very young children. For example, there might be some pain and swelling at the injection site.

Less commonly, fever and aches might occur in children receiving their first flu vaccine.

To protect children, the people around them should also receive flu shots.

Pros and cons for pregnant women

The CDC’s Advisory Committee on Immunization Practices recommend that women get a flu shot during pregnancy.

Pregnant women are at a higher risk of severe illnesses from the flu. For pregnant women, a flu shot can:

  • reduce the risk of acute respiratory infection by half
  • lower the risk of hospitalization from the flu by 40%
  • protect the baby from the flu for several months after birth

The flu shot might still cause some minor side effects, such as nausea and swelling.

There are several strains of the flu, which change every season.

Doctors must try to predict the most common strains of flu each season. They then decide what type of vaccine to use in the flu shot.

All flu shots this year are quadrivalent. These vaccines protect against four strains of the virus.

Children receiving their first flu shot between the ages of 6 months and 8 years should receive a second flu shot 4 weeks afterward.

The table below lists the different types of flu vaccines that are currently available.

Vaccine type How it is given Who it is for How often it is given
quadrivalent injection anyone aged 6 months or older yearly
nasal spray single spray in each nostril anyone aged 2–49 years and not pregnant yearly
jet injector high pressure stream of fluid through the skin people aged 18–64 years yearly
high dose injection people aged 65 years and older yearly
flu vaccine with adjuvant injection people aged 65 years and older yearly
cell-based injection anyone over 4 years of age yearly
recombinant injection anyone aged 18 years and older yearly

The flu is a widespread, seasonal virus. In some people, the flu can lead to severe illness and even death.

The flu shot is a safe way of preventing the flu. The risks of getting a flu shot are small, and any side effects are usually mild. Flu shots are important for protecting vulnerable groups, such as older adults and young children, from severe illnesses.