FluMist (influenza vaccine live, intranasal) is a vaccine used to help prevent flu. FluMist can cause side effects that range from mild to serious. Examples include runny nose, congestion, and fever.

FluMist is approved for use in people ages 2 through 49 years to help prevent flu.

The active ingredient in FluMist is influenza vaccine (live). The drug comes as a nasal spray that’s given by a healthcare professional.

Keep reading to learn about common, mild, and serious side effects that FluMist can cause. For a general overview of the drug, including details about its uses, see this article.

Some people may experience mild to serious side effects after receiving FluMist. Examples of FluMist’s commonly reported side effects include:

You can learn more about congestion and fever in the “Side effects explained” section.

The list above includes only a few of the side effects possible with FluMist. Keep reading to learn more about side effects of FluMist. Each person’s experience with side effects may differ.

Mild side effects have been reported with FluMist. These include:

In most cases, these side effects should be temporary. And some may be managed easily. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist.

FluMist may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Serious side effects have not been reported with FluMist. But this doesn’t mean they can’t occur or won’t be identified later.

If you think you’ve developed serious side effects after receiving FluMist, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911. Or call your local emergency number.

Note:After the Food and Drug Administration (FDA) approves a vaccine, it and the Centers for Disease Control and Prevention (CDC) track side effects of the drug. If you’d like to report a side effect you’ve had with FluMist, visit the Vaccine Adverse Event Reporting System (VAERS) website.

Allergic reaction

For some people, FluMist can cause an allergic reaction. But it’s not clear whether this side effect occurred in the drug’s studies.

In general, symptoms of an allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms. They also can determine whether you should ever receive FluMist again.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

Your doctor can confirm whether you’ve had a serious allergic reaction to FluMist. If so, they may have you switch to a different flu vaccine for you to receive next time.

Get answers to some frequently asked questions about FluMist’s side effects.

How do side effects of FluMist nasal flu vaccine compare with side effects of an injection flu shot, such as Fluzone?

FluMist and Fluzone both are vaccines used to help prevent flu. They contain different active ingredients, and you receive each in a different way.

FluMist is a live vaccine that you receive as a nasal spray. (A live vaccine contains a weakened version of the bacteria or virus it’s meant to protect against.) Fluzone is an inactivated vaccine that you receive as an injection into your muscle. (Inactivated vaccines contain bacteria or viruses that aren’t living.)

Because of these differences, the side effects of each vaccine may differ.

Side effects of FluMist are discussed previously in this article. For injected vaccines, such as Fluzone, typical side effects include:

  • injection site reaction
  • muscle pain
  • headache
  • fatigue

To learn more about the side effects of FluMist and Fluzone, talk with your doctor or pharmacist. You can also read this article for more details about Fluzone’s side effects. If you’d like information on FluMist Quadrivalent (also a nasal spray), ask your doctor or pharmacist.

How do side effects of FluMist in children compare with side effects in adults?

FluMist is used to help prevent flu in children ages 2 years and older. In studies of FluMist, side effects in children were similar to side effects in adults. But children also experienced fever over 100°F (37.8°C) and abdominal pain.

Some children are at higher risk of breathing problems after receiving FluMist. These include children younger than ages 5 years with asthma or other breathing conditions. Be sure to tell your child’s doctor if your child has any breathing problems before they receive FluMist. The doctor may recommend that your child get the flu shot instead.

If you have more questions about the side effects of FluMist in children, talk with your doctor or pharmacist.

How long after a dose of FluMist (nasal flu vaccine) do side effects occur?

If side effects occur after a dose of FluMist, they typically start soon after the vaccination. In most cases, side effects are temporary and will go away after a few days.

Talk with your doctor or pharmacist if you have more questions about side effects of FluMist. Also talk with them if you’re experiencing ongoing side effects from the vaccine.

Learn more about some of the side effects FluMist may cause.

Congestion

Congestion was a common side effect reported in studies of FluMist. Congestion refers to a stuffy nose. It may cause symptoms such as:

  • swollen nasal tissue
  • stuffy nose
  • sinus pain

What might help

If you have congestion after receiving FluMist, consider trying home remedy options. These might help relieve your symptoms:

You may also consider over-the-counter medications that can include:

Before taking any new medications, it’s important to talk with your doctor. They can discuss which options are safest for you.

Fever

Fever was a common side effect reported in studies of FluMist.

A fever describes a body temperature that’s higher than usual. A typical body temperature is around 98.6°F (37°C). Studies of FluMist define fever as a body temperature above 100°F (37.8°C).

In some cases, other symptoms may accompany a fever, such as:

  • shivering
  • headache
  • muscle aches
  • weakness
  • sweating
  • loss of appetite
  • dehydration

What might help

Sometimes a fever will go away with rest and fluids. Other things that can help include:

In some cases, a fever requires medical attention. Examples of when you should call your doctor include:

  • Your child has a fever above 102.2°F (39°C).
  • You or your child has had a fever for more than 3 days.
  • You have a serious medical condition or a weakened immune system.
Keeping track of side effects

Following your FluMist vaccination, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first receive a new vaccine.

Your side effect notes can include things such as:

  • what dose of the drug you had received before you had the side effect
  • how soon you had the side effect after receiving that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Sharing notes with your doctor will help them learn more about how FluMist affects you. They can then use this information to adjust your vaccination plan if needed.

The following is important information you should consider before receiving FluMist.

Warnings

FluMist can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether FluMist is a good vaccination option for you.

Talk with your doctor about your health history before you receive FluMist. Be sure to tell them if any of the following factors apply to you:

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.