Childhood Vaccines: What is in the Vaccines and Why

HealthLinkBC File Number: 
Child Immunization Series
Last Updated: 
January 2016

Immunization has saved more lives in Canada in the last 50 years than any other health measure.

What is in childhood vaccines?

Vaccines are made with ingredients that make them safe and effective to protect your child from disease.

Each vaccine contains a small amount of the disease germ (virus or bacteria) or parts of the germ. Examples are the measles virus, pertussis (whooping cough) bacteria, and tetanus toxoid. Vaccines do not cause disease because the germs are either dead or weakened and the toxoids are inactive. Vaccines help your child’s immune system build protection against disease.

Other ingredients in vaccines help keep them stable and prevent contamination of multi-dose vials by bacteria and fungi. Some vaccines have ingredients to boost the immune response to the vaccine.

Why are some of the other ingredients in vaccines?

To keep vaccines safe and effective, they contain ingredients such as aluminum salts, antibiotics, and formaldehyde. These ingredients have not been linked to disease or illness. Below are some of the ingredients in vaccines.

Antibiotics — Antibiotics are used in some vaccines to prevent bacterial contamination when the vaccine is being made.

Aluminum salts — Aluminum salts have been used in vaccines for many years. They improve the body’s immune response to the vaccine, giving you better protection from disease.

Children are naturally exposed to aluminum in the environment. Aluminum is found in the air, food and water. It is even in breast milk and infant formula. The amount of aluminum in a vaccine is similar to that in the infant formula a baby may drink in a day.

Formaldehyde — Some vaccines are made from live germs or toxins, which need to be killed or made inactive so they do not cause disease. Formaldehyde is used to do this, and then it is removed. Any tiny amount left in the vaccine will not harm your child.

Other ingredients — Sugars, amino acids, salts, and proteins, such as albumin and gelatin, help keep vaccines stable and safe when they are being made, shipped and stored.

Do childhood vaccines contain thimerosal?

In B.C., thimerosal has not been used in any routine childhood vaccine since 2001, except for the influenza or flu vaccine. Thimerosal is a mercury-containing preservative that is in the flu vaccine in small amounts to prevent bacterial and fungal growth. If a person received a vaccine contaminated with bacteria or fungi, they could get sick.

A large number of studies have shown no link between the use of vaccines containing thimerosal and harm to children. These studies are posted at the Institute of Medicine of the National Academies

Do vaccines contain human or animal cells?

No. Vaccines do not contain human or animal cells. The viruses needed to make some vaccines can only be grown in human or animal cells. After the virus has been grown, it is separated from the cells and used to make the vaccine. So while human or animal cells may be used in the earlier stages of making the vaccine, no cells are present in the final product or vaccine.

Which vaccines contain egg protein and why?

The MMR (measles, mumps and rubella) vaccine and the influenza (flu) vaccines contain egg protein. Egg protein is present in these vaccines because the viruses used to make them are grown in eggs (flu vaccine) or in cells taken from eggs (MMR vaccine). The amount of egg protein in the MMR vaccine is not harmful for children with egg allergies.

The influenza vaccines available in B.C. are either inactivated or live attenuated vaccines. All influenza vaccines currently available in Canada are produced using eggs. The inactivated influenza vaccines have been well studied in people with allergy to eggs including those with severe allergies. These inactivated vaccines can be safely given to people with egg allergies, and are given by injection. The safety of the live attenuated influenza vaccine (given by nasal spray) in people with egg allergies has not been well studied. If you have an allergy to eggs, you should not get the live attenuated influenza vaccine.

There is an extremely rare possibility, less than one in a million, of a life-threatening allergic reaction after getting a vaccine. If this happens, it is most likely to occur within minutes after the vaccine is given. This is why you are asked to stay at the clinic or health care provider’s office for 15 minutes after your child has been immunized. Your healthcare provider is prepared to treat this reaction.

For More Information

For more information on immunizations, visit ImmunizeBC

For more information on childhood immunization, see:

ImmunizeBC logo BCCDC logo

Is it an emergency?

If you or someone in your care has chest pains, difficulty breathing, or severe bleeding, it could be a life-threatening emergency. Call 9-1-1 or the local emergency number immediately.
If you are concerned about a possible poisoning or exposure to a toxic substance, call Poison Control now at 1-800-567-8911.

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