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Flu Vaccines

What is a flu vaccine?

A flu vaccine protects people from developing influenza (flu). Flu is a contagious respiratory (breathing) illness. A flu vaccine causes a person to develop antibodies that recognize and fight flu viruses. This builds up the body’s natural defenses (immunity) against infection.

People need a flu vaccine once a year. This is because the vaccine is different each year. Flu viruses change over time, so the vaccine from last year may not work as well for the next year. Also, your body’s immune response decreases over time.

Find more information on influenza (flu)

Illustration of girl wearing mask and a bandaid on arm for flu shot. Text says, "Help prevent the flu: Get your flu vaccine"

An annual flu vaccine is one of the best ways to prevent the flu.

Benefits of the flu vaccine

A vaccine strengthens the immune system to protect the body from illness. The flu vaccine helps protect people from developing the flu. Some people may still get the flu after being vaccinated. Even if you do get the flu, you may not get as sick. This is because your body is better able to defend itself after getting the vaccine.

Most people who get flu get better in a few days to less than 2 weeks. But some people develop more serious problems or complications. Some problems can be life threatening.

Sinus and ear infections are examples of moderate complications from the flu. Pneumonia is an example of a serious flu complication.

Flu vaccination is especially important for people with certain medical conditions, including:

  • Asthma
  • Heart disease
  • Diabetes

The flu can make these medical problems worse. For example, people with asthma may get asthma attacks while they have the flu. People with heart disease may have an increased heart attack risk because of the flu.

Types of flu vaccine

There are 2 main ways the flu vaccine is given:

Flu shot (needle injection):

  • There are several different types of flu shots. Most are given in the muscle of the upper arm. Infants and very young children may get the flu shot in the upper thigh.
  • The flu shot is made with dead (inactivated) flu viruses.
  • The flu shot is safe for people with weak immune systems.
  • If your child has a weakened immune system, your child can take it at least 2 weeks before chemotherapy for the best response to the vaccine. Or they can take it between chemotherapy cycles. In the case of a spreading flu illness, your child should get a flu shot as soon as possible with no delay.

Nasal spray (Flumist®):

  • The nasal spray form of the flu vaccine has a weakened live form of the flu virus.
  • If your child has a weakened immune system, they should not get the nasal spray form of the vaccine. People in the same household as your child should not get the nasal spray either.

Your health care provider will recommend the best flu vaccine for your child.

Possible side effects of the flu vaccine

Mild side effects are normal after a flu vaccine. Symptoms may include:

  • Redness or swelling at the injection site
  • Headache
  • Fever
  • Fatigue
  • Nausea
  • Body aches

Flu vaccines do not give you the flu. Side effects are usually mild and go away after a few days. This is because the immune system is responding to the vaccine. The body is making antibodies against the flu.

When to get the flu vaccine

If possible, get the flu shot in September or October, or as soon as it becomes available. If you don’t get a flu shot early, getting one any time during the flu season will help protect you. In general, flu cases in the U.S. start to rise in October, peak in December through February, and can last until May.

It takes about 2 weeks to develop an immune response after getting the flu vaccine. In certain cases, children may need 2 doses of the flu vaccine. Your health care provider will tell you if another dose is needed.

Flu vaccines in children with weak immune systems

Medical experts advise that most children with serious illnesses and all children 6 months and older get yearly flu shots. The Centers for Disease Control and Prevention, the American Academy of Pediatrics, and the Infectious Diseases Society of America agree on this advice. It is important to remember that the vaccine is usually not harmful.

Ask your child’s care team when to give your child the flu vaccine. Your child might not respond to the flu vaccine if they have had:

  • Strong chemotherapy
  • Anti B-cell antibodies within 6 months

Transplant, cellular (CAR T-cell) therapy, and gene therapy patients can get a flu shot 6 months after their infusion. If there is a flu outbreak in the community, they can get a flu shot 4 months after transplant.

Depending on your child’s diagnosis and treatment plan, the care team will advise when your child should get the flu shot. Talk to your child’s care team about your child’s specific situation.

Flu vaccines for family members

If you have a child with a serious illness, it is important for family members and those in close contact with your child to get the flu vaccine. Young children and those with serious illnesses are at higher risk for life-threatening complications from the flu.

Getting all family members and caregivers vaccinated helps to create a circle of protection around your child.

“The most important thing I want people to remember is to get the flu shot as soon as possible, and to make sure that everyone around a patient gets the vaccine as well. Let’s create a circle of protection around our patients as we protect ourselves.”

Hana Hakim, MD, MS

Flu vaccines and egg allergies

The Centers for Disease Control and Prevention (CDC) recommend that everyone 6 months and older with an egg allergy should get the flu vaccine. Any flu vaccine (egg based or non-egg based) can be used.

The flu and COVID-19 

It is possible to have both the flu and COVID-19 at the same time. Both COVID-19 and the flu are respiratory infections. The symptoms of COVID-19 and the flu can be the same.

The flu vaccine will not protect you from COVID-19. And the COVID-19 vaccine will not protect you from the flu.

If you have symptoms, your care team will likely test for both illnesses. The test results can help your care team decide the best treatment.

Questions to ask your care team about flu vaccines

  • Is the flu vaccine safe for my child?
  • What type of flu vaccine is best for my child?
  • Are there any vaccines my child should not get?
  • Does my child need 2 doses of flu vaccine?
  • What are the side effects of the flu vaccine?
  • What should we expect before, during, and after getting the flu vaccine?
  • Are there any warning signs of severe side effects that I should watch for?
  • If my child is in treatment for a serious illness, when is the best time for my child and my family to get a flu vaccine?
  • How can I protect my child if they are not able to get a flu vaccine?

More information about flu and flu vaccines

Key points about flu vaccines

  • The flu vaccine is a safe and effective way to help prevent the flu.
  • Types of flu vaccine include the flu shot and nasal spray.
  • A flu vaccine is generally recommended for all people ages 6 months and older.
  • If your child has a serious illness or a weak immune system, talk with your care team about the flu vaccine.
  • If your child has a weak immune system, all caregivers and household members should get a flu vaccine to help protect your child from illness.

TheTogether by St. Jude online resource does not endorse any branded product mentioned in this article.

Reviewed: January 2024