Side Effects of the Influenza Vaccine

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, many people experience mild side effects to the flu shot (intramuscular injection) or nasal spray flu vaccine.

Common Influenza Vaccine Side Effects

Overall, the annual influenza vaccine offers safe and effective protection against the seasonal flu. The side effects you may experience from the flu vaccine are typically mild and are due to an immune system response that boosts your immunity against the virus.

Common side effects are similar for both the shot and nasal spray and include:

• Low-grade fever
• Headache
• Muscle aches

In terms of the most common side effects by vaccine type:

Flu Shot Side Effects

Inactivated flu shots (what's typically given) contain flu viruses that have been killed and are, therefore, not infectious. Side effects can include:

• Pain at the injection site
• Redness and swelling at the injection site
• Headache
• Fatigue or malaise (feeling tired)
• Red or itchy eyes
• Hoarse voice
• Cough
• Fever

Nasal Spray Side Effects

Live attenuated influenza vaccines (LAIV) are used in the nasal spray (FluMist Quadrivalent). This vaccine uses a live virus that has been weakened and will not cause influenza illness. The attenuated virus is cold-adapted and can only multiply at cooler temperatures, like those in the nose biome, and cannot survive at body temperature.

Side effects can include:

• Runny nose, congestion, or cough
• Fever
• Headache or muscle aches
• Wheezing (typically in children)
• Abdominal pain or occasional vomiting or diarrhea (typically in children)
• Sore throat
• Weakness or fatigue (feeling tired)

Rare Side Effects

Though rare, serious allergic reactions including anaphylaxis may occur. Signs of anaphylaxis include:

• Itching
• Red, raised, blotchy skin
• Swollen tongue, lips, or throat
• Wheezing or shortness of breath

Anyone who has experienced an allergic reaction to a flu vaccine in the past should not receive one in the future.

Egg Allergies

If you have an egg allergy, be sure to tell your doctor before getting the flu shot. The allergy, however, should not prevent you from getting vaccinated.

For many years, flu shots were not recommended for people with egg allergies because the vaccine was initially grown in chicken eggs, posing a risk of an allergic reaction.

But new recombinant flu vaccines, such as Flublok Quadrivalent (for adults 18 years and older) and Flucelvax Quadrivalent (for people 4 years and older), are manufactured without using eggs and are safe for people with egg allergies.

As of the 2016 to 2017 influenza season, the U.S. Centers for Disease Control and Prevention (CDC) recommends the flu vaccine for people who have a history of egg allergy. However, people with a history of severe allergic reactions to eggs should be sure to get the flu shot from their doctor, who can spot signs of a severe allergic reaction and can manage those symptoms if they occur.

People With Chronic Conditions

While 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. The nasal spray, on the other hand, is not recommended for certain individuals.

The CDC highly recommends the annual flu shot for those who are at higher risk of complications from influenza, which includes people with:

• Asthma
• Diabetes
• Heart disease
• Sickle cell disease
• Kidney or liver disease
• neurologic or neuromuscular disorders
• metabolic disorders
• A weakened immune system due to diseases such as HIV, AIDS, and certain cancers, or immune-suppressing medications, such as chemotherapy, radiation treatment, or corticosteroids

Injectable influenza vaccines have a long, established safety record in people with diabetes, asthma, cancer, heart disease, compromised immunity, and other chronic health conditions.

The LAIV nasal spray vaccine is not recommended for people with chronic health conditions. The nasal spray contains a weakened form of the live influenza virus and should not be used in people with weakened immune systems.

People with asthma are at an increased risk for wheezing after getting the nasal spray flu vaccine, and children 2 to 4 years old who have asthma or who have had a history of wheezing in the past 12 months should not get the nasal spray vaccine.

Vaccine Safety and Autism

Some people have concerns that the flu vaccine may cause autism. Preservatives, such as thimerosal, are used to prevent bacteria or fungi from contaminating vaccines that are packaged in multi-dose vials.

Thimerosal, an ethyl mercury-based preservative, was once considered a possible trigger for autism. However, research shows this is not the case. According to the CDC, thimerosal use in vaccines has a record of being very safe and data from many studies show no evidence of harm caused by the low doses of thimerosal in vaccines.

If you are concerned about preservatives in the flu vaccine, talk to your doctor. Most single-dose vials and pre-filled syringes of the flu shot and the nasal spray flu vaccine do not contain a preservative because they are intended to be used once.