Health Topic

Flu Shot

The flu shot causes your body to develop antibodies against influenza viruses. Know more about getting vaccinated against getting the flu.

Reviewed Reviewed by a registered pharmacistGeneral information

Also called: Flu vaccine

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Flu Shot

The flu (influenza) is a respiratory infection. It is caused by influenza viruses that infect your nose, throat, and lungs. These viruses can spread from person to person.

Most people with the flu get better on their own, without medical care. But for some people, the flu is serious. It can cause complications and sometimes even death. People who are 65 and older, under age 5, pregnant, or have certain health conditions are at higher risk of flu complications.

Getting vaccinated against the flu each year is best way to lower your risk of the flu and its complications.

There are many reasons to get a flu shot each year:

  • It may keep you from getting sick with the flu.
  • If you do get the flu, it may be less severe. You may also be less likely to have complications or need to be hospitalized with the flu.
  • If you have certain chronic health conditions, getting a flu shot may help prevent the flu from making your condition worse. For example, if you have COPD or diabetes, the flu can worsen your condition so much that you might need to be hospitalized. Getting a flu shot can lower this risk.
  • Getting the vaccine during pregnancy not only helps protect you from the flu during and after pregnancy. It also helps protect your baby from flu during their first few months of life.
  • It has been shown to lower the risk of severe life-threatening flu in children.
  • It may also protect the people around you, including those who are at higher risk of complications.

The flu vaccine causes your immune system to make antibodies about two weeks after you get the shot. These antibodies provide protection against infection with the flu viruses that are in the vaccine.

The U.S Centers for Disease Control and Prevention (CDC) recommends annual flu shots for everyone 6 months and older, with a few rare exceptions.

Flu shots are especially important for people who are at high risk of developing serious complications from the flu.

There are different types of flu vaccines. There are injectable vaccines (shots) and nasal spray vaccines. There are also some vaccines especially for people 65 and older. Ask your health care provider which one is right for you.

There are some people who should not get a flu shot:

  • Children younger than 6 months of age.
  • Have severe, life-threatening allergies to flu vaccine or any ingredient in the vaccine. This might include gelatin, antibiotics, or other ingredients.

Some people need to talk to their provider before they get a flu shot. They include people who:

  • Have an allergy to any of the ingredients in the vaccine.
  • Have ever had Guillain-Barre syndrome(GBS). Some people with a history of GBS should not get a flu vaccine.

If you are moderately or severely ill, you usually need to wait until you recover before getting a flu shot.

You need to get a flu shot every year because:

  • Your immune protection from the vaccine declines over time. You need to get the shot every year to boost that protection.
  • Flu viruses are constantly changing, so every year, the flu vaccine is updated. The flu vaccine will include protection against the viruses that will most likely be common during the upcoming flu season.

For most people who need only one dose of the flu vaccine for the season, September and October are usually good times to get it. It's best to be vaccinated by the end of October.

Some children need two doses of the flu vaccine. They should get their first dose as soon as the vaccine is available. They need to get the second dose at least four weeks after the first.

If you are pregnant, talk to your provider about when to get the vaccine. When you should get it can vary, based on how far along you are in your pregnancy.

Flu vaccines have been shown to be safe. But like any medical product, they can cause side effects. If you have any side effects, they are usually mild and go away on their own within a few days. Common side effects include:

  • Soreness, redness, and/or swelling from the shot
  • Headache
  • Fever
  • Nausea
  • Muscle aches

The flu shot, like other injections, can occasionally cause fainting. In rare cases, some people have a serious allergic reaction.

Centers for Disease Control and Prevention

It sits within Immune System.

The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Flu Shot

1,478 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

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Related Issues

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Influenza Vaccines. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Flu Shot, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.