Side Effects of the Influenza Vaccine

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The influenza vaccine is the best protection against seasonal flu, which is why millions of people get the flu shot each year. While very few serious side effects have been reported, people have been known to experience mild side effects to the flu shot or nasal spray flu vaccine (FluMist).

Boy getting flu shot
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Common Side Effects

The annual influenza vaccine offers safe and effective protection against the seasonal flu. The side effects are typically mild and due to an immune response that effectively boosts your immunity to the virus.

Side effects common to both the flu shot and FluMist nasal spray include:

There are also side effects specific to the flu shot and FluMist nasal spray. For example, cough can occur after the administration of FluMist.

Flu Shot Side Effects

Flu shots involve inactivated viruses that have been killed and are not infectious. Side effects can include:

  • Pain at the injection site
  • Redness and swelling at the injection site

FluMist Side Effects

The FluMist nasal spray is a live attenuated influenza vaccine (LAIV) made with live viruses that have been weakened and are unable to cause influenza illness. The attenuated viruses can only multiply at cooler temperatures, like those in the nose, and cannot survive at body temperature.

Side effects can include:

Despite a common myth that the flu vaccine can give you the flu, neither the flu shot nor the flu nasal spray will infect you with influenza.

Rare Side Effects

Although rare, serious allergic reactions including anaphylaxis may occur following vaccination. Signs of anaphylaxis include:

Anaphylaxis is considered a medical emergency and, if left untreated, can lead to unconsciousness, shock, coma, heart or respiratory failure, and death.

Anaphylaxis typically occurs within five to 30 minutes of coming into contact with an allergy-causing substance (allergen), although some cases can take more than an hour.

A study from the Centers for Disease Control and Prevention (CDC) found the rate of anaphylaxis after all vaccines is 1.31 per one million doses.

Anyone who has experienced a severe, life-threatening allergic reaction to a flu vaccine in the past should not receive one in the future. Of note, people who have had a mild allergic reaction (such as hives the next day) can and should continue to receive the annual flu vaccine.

Egg Allergies

For many years, flu shots were avoided by people with egg allergies because the vaccine was initially grown in chicken eggs, posing a potential risk for a reaction.

New recombinant flu vaccines—such as Flublok quadrivalent (for adults 18 and older) and Flucelvax quadrivalent (for people 4 years and older)—are manufactured without eggs, making them safe for people with egg allergies.

While you should tell your healthcare provider if you have an egg allergy before getting the flu shot, know that this should not prevent you from getting the vaccination.

The risk of an allergic response to any flu vaccine is extremely low—including those that are egg-based. As such, the CDC recommends the vaccine even for people who have a history of egg allergies or have experienced mild hives following vaccination.

Those with a history of severe allergic reactions to eggs should get the flu shot from their healthcare provider, who can spot signs of a reaction and manage the symptoms quickly.

Flu Shot and Chronic Conditions

Although people with chronic health conditions are at a greater risk of complications from the flu, they are at no greater risk for side effects from a flu shot. Injectable flu vaccines have an established safety record in this vulnerable population of people.

However, the FluMist nasal spray vaccine is not recommended for people with certain chronic health conditions due to potential complications from the weakened form of the live influenza virus it contains.

Vaccines and Autism

Rumors have long circulated suggesting that the flu vaccine may cause autism. It has been proposed preservatives such as thimerosal are responsible for this effect.

Thimerosal, an ethyl mercury-based preservative, was once considered a possible trigger for autism. Research has shown that this is not the case. According to the CDC, thimerosal has a long history of safety with no evidence of harm caused by the low doses used in vaccines.

If you are concerned about preservatives in the flu vaccine, talk to your healthcare provider about preservative-free options. Most single-dose vials and prefilled syringes do not contain a preservative because the products are used immediately and not shared. The same applies to the FluMist nasal vaccine, which is also preservative-free.

Frequently Asked Questions

  • How long do you feel bad after the flu shot?

    You may feel soreness for a couple of days in the spot where you were injected with the flu vaccine. If you suffer side effects like low-grade fever, headache, fatigue, or muscle ache, your symptoms should go away after a day or two.

  • Do you shed the flu virus after getting the vaccine?

    If you get the live attenuated vaccine, which is in the FluMist nasal spray, it’s possible that you may shed the live virus for up to 11 days after being inoculated. Shedding with this type of vaccine is most common in young children. 

  • Does the seasonal flu vaccine affect your heart?

    In a positive way, yes. Research shows that getting the flu shot can lower your risk of heart attack, heart failure, and other major cardiac events during the following flu season.

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14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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