Allergic Reactions to the Flu Shot

Influenza—also known as the flu—can affect between 3% and 11% of Americans each year. Certain people, like people aged 65 and older or those with chronic conditions like asthma, are at a greater risk of developing serious complications if they get the flu. The best way to stop from getting sick is to get a seasonal flu vaccine.

Flu vaccines come in the form of shots and the FluMist nasal spray. The CDC recommends that most people over six months of age get a flu vaccine each year. Unfortunately, many people opt not to for a variety of reasons, from misinformation about flu shot effectiveness to concerns about possible health risks, side effects, or allergies.

Most common side effects, such as a low-grade fever or a sore arm, shouldn't stop you from getting your annual flu shot. But these symptoms are very different than a true allergy to the flu vaccine itself.

This article outlines important information about flu vaccine side effects, what it means to have a true allergy, and what your risk of an allergic reaction could be.

Side Effects of the Flu Vaccine

It's important to understand that the flu vaccine does not cause the flu. But some people will experience side effects similar to flu symptoms. Most of these are mild and often resolve on their own within a day or two.

Though the flu shot and the FluMist nasal flu vaccine share some side effects, there are also differences:

Side effects, however, are not necessarily symptoms of an allergy or other serious reaction. It's important to understand the difference.

Serious Reactions to Flu Vaccines

Even though serious reactions to the flu vaccine are rare, it's important to recognize the signs and symptoms so that you can get treatment right away. Though both are rare, it is possible to have an allergic reaction to the vaccine, or develop Guillain-Barré Syndrome after.

Allergic Reactions

A true allergy is one in which the immune system produces defensive antibodies to fight off an otherwise harmless substance. Serious allergic reactions can result in anaphylaxis, a potentially life-threatening condition.

FluMist and most flu shots are manufactured using egg-based technology. They contain trace amounts of an egg protein called ovalbumin, a substance that 1.3% of children and 0.2% of adults are allergic to.

However, just because you have an egg allergy doesn't mean you'll have an allergic reaction to FluMist or a flu shot. In fact, the American Academy of Allergy, Asthma and Immunology no longer recommends that people with egg allergies avoid vaccination for flu.

Call 911 or seek emergency care right away if you experience any of the following symptoms after getting your flu vaccine:

• Rash or hives (a small rash at the injection site is not considered a severe allergic reaction)
• Shortness of breath
• Wheezing
• Rapid heartbeat
• Nausea and vomiting
• Swelling of the lips, face, tongue, or throat
• Dizziness and/or fainting
• Confusion
• A feeling of impending doom

While it is possible to have an allergic reaction to a flu vaccine, it's rare. According to the Centers for Disease Control and Prevention (CDC), an allergy to the flu vaccine only affects only one or two people out of every million doses.

Guillain-Barré Syndrome

Even if you don't have a true allergy to the flu vaccine, you may experience a type of reaction that is serious enough to warrant avoiding the shot in the future.

Guillain-Barré syndrome (GBS) is an autoimmune disorder affecting the nerves. It can sometimes be triggered by the flu vaccine, but that is extremely rare. GBS occurs more commonly after a respiratory or gastrointestinal illness.

GBS typically begins with weakness, pain, or tingling in the feet or legs (especially in children). After these initial symptoms calm or disappear, serious long-term symptoms, like weakness on both sides of the body, may suddenly develop and get worse.

Other symptoms of GBS include:

• Loss of coordination and unsteadiness
• Difficulty speaking, swallowing, or chewing
• Difficulty with eye muscle control
• Vision problems
• Difficulty breathing
• Irregular heartbeat
• Severe neuropathic pain, especially at night
• Digestion problems
• Loss of bladder control

Even though most people (about 70%) with GBS fully recover, it can take a long time. More severe cases can result in permanent muscle weakness or even paralysis.

It is rare to develop GBS after a flu shot. If you've had GBS after a previous flu vaccination, speak with your healthcare provider to discuss your risk and what other options are available for you.

What You Can Do

If you have a known egg allergy and have experienced severe symptoms in the past, after being vaccinated for the flu, talk to your healthcare provider about two egg-free flu shots approved by the FDA:

• Flublok quadrivalent (for use in adults 18 years and older)
• Flucelvax quadrivalent (for use in people 4 years and older)

Any severe allergic reaction to a flu vaccine, whether it contained egg protein or not, is serious. Talk to your doctor about whether it would be safe to consider a flu vaccine in the future.

A Word From Verywell

Serious reactions to the flu shot—including allergies—are extremely rare. The potential risk should not deter you from getting the vaccine. Rather, you should share your concerns with your healthcare provider, who can help you determine whether the flu vaccine is right for you.

If you experience adverse symptoms of any kind after either the flu shot or FluMist, contact a healthcare provider to seek the proper treatment.