The Most Common and Rare Flu Shot Side Effects

The flu shot is the best protection against seasonal flu. This is why millions of people get the influenza vaccine each year. According to the World Health Organization, the seasonal flu infects up to 1 billion people annually.

While very few serious side effects have been reported, people have been known to experience mild flu shot side effects, as well as to the nasal spray flu vaccine (FluMist).

Common Side Effects

Flu shots are produced by using inactive viruses. This means they have been killed and are not infectious. An annual flu shot offers safe and effective protection against the seasonal flu. The side effects are typically mild. They are caused by the immune response that boosts your immunity to the virus.

Side effects may include:

• Low-grade fever
• Headache
• Muscle aches
• General fatigue (malaise)
• Pain, redness, and swelling at the injection site

Rare Side Effects

In very rare cases, people may have serious allergic reactions including anaphylaxis after getting the vaccine.

Signs of anaphylaxis include:

• Rash or hives
• Wheezing
• Shortness of breath
• Rapid heartbeat
• Swollen tongue, lips, or throat
• Dizziness or lightheadedness
• Confusion
• A feeling of impending doom

Anaphylaxis is a medical emergency. If left untreated, it can lead to loss of consciousness, shock, coma, heart or respiratory failure, and death.

This severe reaction typically occurs within five to 30 minutes of contact with an allergy-causing substance (allergen). In some cases, symptoms may appear more than an hour later.

Anyone who has experienced a severe, life-threatening allergic reaction to a flu vaccine in the past should not get the vaccine again 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, people with egg allergies avoided flu shots. This is because the vaccine was initially produced using chicken eggs, posing a potential risk for a reaction.

New recombinant or cell culture-based flu vaccines are made without eggs, making them safe for people with egg allergies. They include Flublok (for adults 18 and older) and Flucelvax (for people 6 months and older).

You should tell your healthcare provider if you have an egg allergy before getting the flu shot. Still, it's important to know that this should not prevent you from getting the vaccine.

The risk of an allergic response to any flu vaccine is extremely low. This includes vaccines that are egg-based. As such, the CDC recommends the vaccine even for people who have a history of egg allergies or who have had mild hives after vaccination.

People with a history of severe allergic reactions to eggs can get the flu shot at their healthcare provider's office, although the CDC no longer recommends additional safety measures for people with egg allergies. The provider can watch them for signs of a reaction and manage the symptoms quickly.

FluMist Side Effects

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

There are some side effects specific to the FluMist nasal spray. Side effects of the nasal spray can include:

• Runny nose and nasal congestion
• Wheezing (typically in children)
• Nausea or vomiting
• Sore throat

There is a common misconception that the flu vaccine can give you the flu. This is not true, and neither the flu shot nor the flu nasal spray will infect you with influenza.

Vaccines and Autism

For years, there have been rumors to suggest the flu vaccine may cause autism. One of the claims is that preservatives such as thimerosal are 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. There is 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 other options. Most single-dose vials and prefilled syringes do not contain a preservative. This is because the products are used right away and not shared. The same applies to the FluMist nasal vaccine, which is also preservative-free.

Summary

An annual flu vaccine is safe and effective for preventing influenza. Many people report mild side effects, like muscle aches or low-grade fever, after getting the shot or nasal spray. These side effects are normal and do not mean that the vaccine gave you the flu. They typically go away in a day or two.

Some people with allergies, notably to eggs, need to be aware of the possibility of a reaction. Recombinant vaccines are an option because they are produced differently. People who have had a severe reaction to the flu vaccine should not receive it again.