FluMist (influenza vaccine live, intranasal) is a brand-name vaccine used to help prevent influenza (flu) in certain adults and children. As with other drugs, FluMist can cause side effects, such as runny nose and headache.

Healthcare professionals may refer to FluMist as FluMist Trivalent. This is because the vaccine guards against three types of the flu virus. There used to be a version of the vaccine — FluMist Quadrivalent — that guarded against four types of the flu virus.

But this version is no longer available. According to the Centers for Disease Control and Prevention (CDC), all U.S. flu vaccines will be trivalent for the 2024 to 2025 season.

Some FluMist nasal spray vaccine side effects are more common than others. The side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who received FluMist in clinical trials:

Mild side effects can occur with FluMist. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to the vaccine’s prescribing information.

Mild side effects that have been reported with FluMist include:

  • cough
  • decreased appetite
  • headache
  • lethargy
  • runny or stuffy nose
  • sore throat
  • tiredness or weakness
  • muscle aches

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you develop a side effect after receiving FluMist and want to tell the FDA about it, you can do so online via the Vaccine Adverse Event Reporting System (VAERS) or call 800-822-7967. You can also contact the vaccine’s manufacturer (MedImmune) at 877-633-4411.

FluMist may cause serious side effects, but they aren’t common. There were no reports of serious side effects in clinical trials of FluMist. The serious side effects listed below have been reported after the vaccine was approved. For more information, you can refer to the FluMist prescribing information.

If you develop serious side effects while taking 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 your local emergency number.

Serious side effects and their symptoms include:

  • pericarditis (inflammation of the sac that surrounds the heart), which may include symptoms such as:
    • chest pain, which may get worse when lying down or coughing
    • cough
    • fatigue
    • heart palpitations (fast, pounding, or irregular heartbeat)
    • shortness of breath when lying down
  • vaccine-associated encephalitis (inflammation of the brain), which may include symptoms such as:
  • Bell’s palsy (see “Side effect specifics” for details)
  • Guillain-Barré syndrome (see “Side effect specifics” for details)
ALLERGIC REACTION

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

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

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to FluMist, your doctor may recommend taking a different medication instead.

FluMist may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

How do the side effects of FluMist vs. flu shot compare?

Side effects of FluMist and the injection form of the flu vaccine (Fluzone, Afluria, others) are similar. Both kinds of vaccine can cause headache, muscle aches, and other flu-like symptoms.

Because the flu shot is an injection, it’s possible to have a reaction at the injection site. This typically includes soreness, redness, or swelling in the area where the injection was given. If you’d like more information, you can read this article about flu shot side effects.

Talk with your doctor about the flu shot and FluMist nasal flu vaccine pros and cons. Together, you can decide which one is best for you.

Note: The FDA has approved FluMist for use only in people ages 2 through 49 years. If you’re in a different age group, your doctor will likely recommend getting a flu shot. For more information, talk with your doctor or pharmacist.

How long after the nasal flu vaccine do side effects start?

In people receiving FluMist in clinical trials, side effects started within 10 to 14 days. Side effects from FluMist are generally expected to be mild and short term, lasting only a few days. See the “More common side effects of FluMist” section for details.

If you have side effects that persist or bother you, talk with your doctor or pharmacist. They’ll be able to recommend some ways to relieve your symptoms.

Learn more about some of the side effects that FluMist may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for FluMist.

Bell’s palsy

Bell’s palsy wasn’t reported in clinical trials of FluMist but it was reported after the vaccine became available.

Bell’s palsy is a sudden weakness or paralysis of the facial muscles on one side of your face. Symptoms may include:

  • drooling
  • drooping of one side of your face
  • headache
  • jaw or ear pain on the affected side of your face
  • trouble closing the eye on the affected side of your face
  • uneven smile

Bell’s palsy is rare but typically happens after a viral infection or a vaccination that irritates or inflames the nerve that controls the facial muscles.

What you can do

Call your doctor if you have symptoms of Bell’s palsy. They can recommend treatments to help ease your symptoms and speed recovery. Symptoms typically improve over a few weeks to months.

Guillain-Barré syndrome

There were no reports of Guillain-Barré syndrome in FluMist clinical trials, but it has occurred after the vaccine became available.

Guillain-Barré syndrome is a nerve condition that causes numbness, weakness, or paralysis. Symptoms may include:

  • unusual sensations in your hands or feet
  • muscle pain or cramps
  • trouble speaking, swallowing, or moving your eyes
  • trouble walking or moving your body

Guillain-Barré syndrome is a rare condition. When it occurs, it typically starts after a viral infection or a vaccination, although there are other causes.

What you can do

Guillain-Barré syndrome can become serious in some cases. Call your doctor right away if you have symptoms of the condition. They can recommend treatments to help you feel better and recover. A full recovery can take several months.

Below is important information you should consider before receiving FluMist.

Before you receive FluMist, discuss your health history with your doctor. FluMist may not be right for you if you have certain medical conditions or other factors affecting your health because it’s unknown if the vaccine is safe and effective.

Be sure to talk with your doctor if any of the following apply to you:

Disclaimer: Medical News Today 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.