Skip to main content

Why do vaccines have so many ingredients? Are they safe?

Image
Common Questions-boy with laptop at school with classmate

Because vaccines are given to millions of babies, children, teenagers, and adults, it’s important that vaccines are shown to be safe and effective. Prior to approval, as part of the U.S. Food and Drug Administration’s (FDA) evaluation, FDA takes all of the ingredients of a vaccine into account.source: 1

Before it grants approval to a vaccine, the FDA requires the vaccine go through a rigorous and extensive development process in a laboratory, as well as animal and human clinical trials. In addition, highly trained FDA scientists and physicians thoroughly evaluate vaccine applications, which contain information like the ingredients in a vaccine.source: 1

  • Some vaccine ingredients are needed to build immunity. Vaccines have antigens, which are either a dead or weakened virus or bacteria, or a piece of virus or bacteria. Some vaccines also have adjuvants, which are substances that promote a strong immune response after vaccination. Both of these ingredients are approved for use in vaccines when they help your immune system respond to and build immunity against a specific disease.source: 2
  • Other vaccine ingredients maintain their quality and help them last a long time. Ingredients called stabilizers help a vaccine work like it's supposed to.source: 3,source: 4 Other ingredients, like preservatives, help keep vaccines free of outside germs and bacteria if multiple doses are given from the same vial.source: 2,source: 3,source: 4
  • Scientists consider vaccine doses and safety when it comes to ingredients. For example, some vaccines contain aluminum salts. These are needed to make vaccines work as they should. Aluminum as a vaccine ingredient has been studied for more than 70 years and found to be safe in approved vaccines.source: 5,source: 6

Key Evidence

  • Vaccine ingredients keep children safe and help vaccines last a long time. Preservatives, for instance, are used in some vaccines to prevent contamination.source: 1 This keeps vaccines safe, helps them work well, and protects those who get vaccinated.source: 2Vaccines help prevent about 4 million deaths worldwide each year.source: 7
  • Vaccines contain ingredients in safe quantities. FDA takes all ingredients into account when evaluating a vaccine's safety and effectiveness.
  • It is rare that a vaccine ingredient causes a serious side effect. Generally, if 1 million doses of a vaccine are given, 1 to 2 people may have a severe allergic reaction to the vaccine.source: 8,source: 9
Image
Common Questions-boy at kitchen table with mother

A Deeper Dive: Vaccine ingredients and their roles

Ingredients That Help Vaccines Provide Immunity

  • Antigens help your immune system recognize and learn how to fight off diseases faster and more effectively. Antigens are either a dead or weakened virus or bacteria or a piece of virus or bacteria.source: 10 Antigens in a vaccine prepare your body to quickly recognize the germ if you come in contact with it in the future.source: 10,source: 11
  • A weakened version of the measles virus is one of the antigens found in the MMR vaccine.source: 12,source: 13 The vaccine uses a very weak virus that cannot replicate very much. The antigens in these vaccines don't make you sick. They help your immune system remember the virus and work to protect against a future exposure of measles, mumps, or rubella.source: 13,source: 14,source: 15
  • Adjuvants are in some vaccines. They help your immune system respond better to a vaccine. This increases your protection against the disease.source: 4,source: 16 Adjuvants have been used safely in vaccines for decades.source: 17
  • Aluminum is an adjuvant. Vaccines made with aluminum have a very small amount in them. It is used to boost immune response. This increases your body’s ability to protect you against the disease.source: 4 Vaccines that include the small amount of aluminum have been used safely for decades. These studies have shown that using it in vaccines is safe.source: 1,source: 18

Learn more about how vaccines provide immunity.

Ingredients That Keep Vaccines Safe and Long-Lasting

  • Preservatives protect the vaccine from outside bacteria or fungus. Today, they are usually used in vials that have more than one dose. Every time a dose is taken from a container, harmful germs could get inside. Most vaccines today are packaged in single-dose containers and do not have preservatives in them.source: 2
  • Thimerosal is a preservative. It prevents germs, bacteria, or fungus from growing in a vaccine.source: 19 With the exception of some flu vaccines, it hasn’t been used in vaccines for children since 2001.source: 19,source: 20 That's because most childhood vaccines are in single-dose containers, so, they do not need a preservative.source: 20 Thimerosal is a type of mercury. It’s a different type of mercury than the dangerous kind (methylmercury) found in some fish. Thimerosal doesn't stay in the body like methylmercury can.source: 19 It has been safely used in vaccines for many years.source: 20
  • Stabilizers help the active ingredients in vaccines continue to work while the vaccine is made, stored, and moved.source: 19 Stabilizers keep the active ingredients from changing because of something like a shift in temperature where the vaccine is stored.source: 2
  • Gelatin is a stabilizer used in vaccines to protect the weakened viruses from freezing or heat. This is especially important during transport and delivery.source: 2,source: 21

Ingredients That Are Used During Manufacturing

  • Cell culture (growth) material helps grow the vaccine antigens.source: 2
  • Inactivating (germ-killing) ingredients weaken or kill viruses, bacteria, or toxins in the vaccine.source: 2,source: 4
  • Formaldehyde is used to weaken or inactivate viruses or bacteria in vaccines.source: 2,source: 4 Only a tiny amount remains once the vaccine is ready to be given to a person. In fact, our bodies naturally have more formaldehyde in them than vaccines made with it do.source: 2
  • Antibiotics help keep outside germs and bacteria from growing in the vaccine.source: 1
  • Streptomycin is an example of an antibiotic used in the production of vaccines.source: 1 It helps prevent vaccines from getting contaminated. Most antibiotics are removed during the process of making vaccines. However, very small amounts may remain in some vaccines.source: 1,source: 2,source: 3 Some children are allergic to antibiotics like penicillin. However, antibiotics most likely to cause severe allergic reactions are not used in vaccines.source: 1

Talk to Your Doctor if Your Child Is Allergic to Antibiotics

If your child is allergic to antibiotics or other vaccine ingredients, then it’s a good idea to talk with their doctor. That way, you can feel confident about your vaccine decisions.

More information

Still have questions? Talk to your child's doctor, nurse, or pharmacist.

Sources

  1. FDA: Common Ingredients in FDA-Approved Vaccines
  2. HHS: Vaccine Ingredients
  3. Children's Hospital of Philadelphia: Vaccine Ingredients
  4. CDC: Vaccine Basics
  5. American Academy of Pediatrics: Vaccine Ingredients: Frequently Asked Questions
  6. CDC: Adjuvants and Vaccines
  7. CDC: Fast Facts on Global Immunization
  8. CDC: Preventing and Managing Adverse Reactions
  9. Journal of Allergy and Clinical Immunology: Risk of anaphylaxis after vaccination in children and adults
  10. CDC: Explaining How Vaccines Work
  11. CDC: Influenza (Flu): Antigenic Characterization
  12. Children's Hospital of Philadelphia: Vaccine Science: How Are Vaccines Made?
  13. CDC: Measles, Mumps, and Rubella (MMR) Vaccination: What Everyone Should Know
  14. The College of Physicians of Philadelphia: What Do Vaccines Do? Different Types of Vaccines
  15. FDA: Vaccines for Children – A Guide for Parents and Caregivers
  16. FDA: Regulatory Considerations in the Safety Assessment of Adjuvants and Adjuvanted Preventive Vaccines
  17. NIAID: Vaccine Adjuvants
  18. Children's Hospital of Philadelphia: Vaccine Ingredients: Aluminum
  19. CDC: Thimerosal and Vaccines
  20. FDA: Thimerosal in Vaccines Questions and Answers
  21. Children's Hospital of Philadelphia: Vaccine Ingredients: Gelatin
  22. CDC: Flu Vaccine and People with Egg Allergies
  23. Children's Hospital of Philadelphia: Vaccine Ingredients: Antibiotics
Back to top
Content last reviewed on

Disclaimer Policy: Links with this icon () mean that you are leaving the HHS website.