The most effective way to prevent the flu — or complications from the flu — is getting your child the flu vaccine. Most children receive the flu shot every year as the Centers for Disease Control and Prevention recommends. But some parents have questions or concerns about the flu vaccine.

Should I Be Concerned About Ingredients in a Flu Shot?

A recent poll found that one in three parents do not plan to vaccinate their children against influenza. The biggest reason for not getting their children the flu shot is concern about side effects. These worries often come from not knowing enough about ingredients in the flu vaccine.

It’s reasonable to have questions about the ingredients in vaccines. Fortunately, the ingredients in flu vaccines have undergone testing for safety in thousands of people. Millions of children safely receive the flu vaccine every year, and studies show that risks related to flu shot ingredients are extremely low.

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What’s in a Flu Shot?

The most important ingredient in a flu vaccine is pieces of the inactivated influenza virus. The virus is cut into pieces in the process of making the vaccine, so it cannot cause the flu. However, when it enters the body through the vaccine, the immune system still recognizes broken flu virus pieces as an intruder.

To fight the intruder, the immune system then produces an army of antibodies. Antibodies are proteins designed to attack a specific germ in the body and then wait in case it comes again. If a real, live flu virus enters the body during flu season, the antibodies attack before the virus can cause disease.

If your child receives the live nasal flu vaccine instead of the shot, it contains a different version of the flu virus. The flu virus in the nasal vaccine is still alive, but the manufacturing process weakens it so much that it can’t cause infection. Again, the body’s immune system doesn’t realize it’s harmless and builds antibodies to remain ready to attack.

Preservatives in Flu Vaccines

Preservatives in a vaccine help prevent other germs, such as bacteria or fungi, from contaminating the vaccine. A common preservative call thimerosal exists in some flu vaccines. Thimerosal has been carefully tested, and studies show that it is very safe.

Possible side effects from thimerosal include redness and swelling at the injection site. A very tiny percentage of people may have an allergy to thimerosal, though this is extremely rare. Thimerosal does not build up in the body and instead breaks down and exits the body.

Single-dose flu shots do not contain thimerosal. Multi-dose flu shots do contain thimerosal to ensure no germs can enter the vial with each new needle.

Stabilizers and Additives

Other compounds called additives, including stabilizer ingredients, ensure that vaccines remain safe and effective during storage. Here are some examples of additive ingredients in flu vaccine:

  • Gelatin is a stabilizer in some vaccines that protects against damaged from heat or freeze-drying for storage. Sugars (such as sucrose or lactose) or artificial sweeteners (like sorbitol) may also be used to keep some vaccines stable and effective.
  • Monosodium glutamate (MSG), the same ingredient found in some Chinese food, is also used in tiny amounts to stabilize some vaccines.
  • Other possible stabilizers include an amino acid called glycine or a protein in blood called albumin. All stabilizers used in vaccines occur naturally in the body or are substances people encounter in everyday life.
  • Polysorbate 80 is a common ingredient found in foods. It ensures that the different ingredients in flu shot vaccines stay separate and evenly spread out.

There may also be tiny amounts of substances leftover from the process of manufacturing the vaccine:

  • Tiny amounts of egg protein might remain in a vaccine after scientists grew the virus in eggs in a lab.
  • Antibiotics, such as neomycin, are added to some vaccines during manufacturing to prevent bacteria from contaminating it in the production process.
  • Formaldehyde is a natural compound made by the human body that’s also used during vaccine manufacturing to inactivate the flu virus. While inhaling large amounts of formaldehyde can cause health problems in people, the trace amounts in a vaccine cannot cause harm. Vaccines contain less formaldehyde particles than the body’s cells naturally produce.

Is the Flu Shot Dangerous or Unsafe?

The flu shot is very safe for people recommended to get it by the CDC. The most common side effects are soreness, redness, or swelling where the injection occurs. Some people may develop a headache, nausea, or a fever from the vaccine, but they typically go away within a few days.

If your child has allergies to gelatin, antibiotics, or another vaccine ingredient, ask your doctor whether your child should get the vaccine. Most antibiotics used in vaccines are not common ones that people have allergies to. Penicillin is not used in making vaccines.

If your child has an egg allergy, they can still safely receive the flu vaccine. There is also one flu vaccine available for children that does not involve growing the virus in eggs. The Flucelvax Quadrivalent flu vaccine is not made with eggs, and people age 4 and older can get it.


Estimates of Flu Vaccination Coverage among Children — United States, 2017–18 Flu Season. National Center for Immunization and Respiratory Diseases. Centers for Disease Control and Prevention. Link

Flu Vaccine and People with Egg Allergies. National Center for Immunization and Respiratory Diseases. Centers for Disease Control and Prevention. Link Vaccine Ingredients: Frequently Asked Questions. The American Academy of Pediatrics. Link

National Poll on Children's Health. Flu vaccine for children in the time of COVID. C.S. Mott Children's Hospital. September 28, 2020. Volume 37, Issue 1. Link

Thimerosal and Vaccines. National Center for Emerging and Zoonotic Infectious Diseases. Centers for Disease Control and Prevention. Link

Understanding Thimerosal, Mercury, and Vaccine Safety. Centers for Disease Control and Prevention. Link

US Food and Drug Administration. Common Ingredients in U.S. Licensed Vaccines. Link

Vaccines & Immunizations. National Center for Immunization and Respiratory Diseases. Centers for Disease Control and Prevention. Link

What's in Vaccines? National Center for Immunization and Respiratory Diseases. Centers for Disease Control and Prevention. Link

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