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Vaccine ingredients

Date last reviewed: 
Tuesday, Jan 30, 2024

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All of the ingredients in vaccines are safe in the amounts used. You may have heard or read that some vaccine ingredients are harmful, but this is true only at much higher amounts than those present in vaccines. Any substance, even water, can be harmful at a high dose. 

What's in vaccines?

The ingredients in vaccines are necessary and are safe in the amounts used.
All vaccine ingredients serve a specific purpose in either making the vaccine, or ensuring that the vaccine is safe and effective. 
This section describes some vaccine ingredients people often ask about, including why they are in vaccines and their safety.  Click on the vaccine ingredient to learn more.
Vaccines contain an antigen (a killed, weakened, or synthetically manufactured version of the disease-causing germ or parts of the germ). Newer vaccines contain instructions for producing the antigen rather than the antigen itself. 
Antigens are considered the active or key ingredients in vaccines because they cause the body’s immune system to respond (they teach the body’s immune system to recognize and attack the real germ).
Aluminum is used as an adjuvant in many vaccines.
Adjuvants enhance the immune response (help the vaccine work better) and allow for fewer quantities of active ingredients and fewer doses of vaccine.
  • Aluminum-containing adjuvants have been used safely in vaccines since the 1930s. That is over 85 years! 
  • Aluminum is one of the most abundant elements. It's in the air we breathe, the water we drink, the food we eat, and many health products.
  • The amount of aluminum in vaccines is extremely small and does not pose a health risk.
  • Infants receive more aluminum from their diet in the first six months of life than from vaccines.
  • Infants quickly remove aluminum from their bodies without harmful effects. 
  • The ability of the body to remove aluminum accounts for its excellent safety record.
    • About half of the aluminum from vaccines is eliminated from the body in less than 24 hours.
    • More than three-quarters is eliminated within two weeks.
  • For aluminum to be harmful, people must have kidneys that don’t work well or at all, and they must receive large quantities of aluminum for months or years.
  • Because large quantities of aluminum can cause serious neurologic effects in humans, Health Canada regulates the amount of aluminum in vaccines. 
  • Health Canada follows standards set by the World Health Organization. It allows for no more than 1.25 mg/dose as a safe level in vaccines.

A graphic demonstrating the amount of aluminum in baby formula, breast milk and vaccines. These amounts are extremely safe.

Formaldehyde is used during the manufacturing process of some vaccines. It is used to kill viruses or inactivate bacterial toxins.
  • The vaccines are purified to remove almost all the formaldehyde. The quantity left in a vaccine does not exceed 0.1 mg. This amount is safe.
  • Formaldehyde is essential in human metabolism and is required for the synthesis of DNA and amino acids (the building blocks of protein). Therefore, all humans have detectable quantities of naturally produced (‘endogenous’) formaldehyde in their circulation.
  • The amount of formaldehyde found in an infant’s circulation is at least ten times greater than that found in any vaccine. 

A graphic demonstrating the amount of formaldehyde in a pear, the amount that naturally circulates in a infant's body, and the trace amount in vaccines. These amounts are extremely safe.

Gelatin is used in some vaccines as a stabilizer.
Stabilizers help prevent ingredients from breaking down while vaccines are being made, stored, and transported. 
  • The gelatin in vaccines is the same material used in many products we eat, such as Jello, marshmallows, and many candies, such as gummy bears. 
  • About one out of every two million people may have a severe allergic reaction to gelatin.
  • The gelatin in vaccines is sourced from cows and pigs.
  • Some religious groups follow dietary rules that prohibit pork products. This has some parents concerned about vaccines that contain gelatin. However, religious groups have approved the use of gelatin-containing vaccines for their followers for the following reasons:
    • Most vaccines are injected, not consumed (exceptions are some oral vaccines, such as the rotavirus vaccine, which does not contain gelatin).
    • The gelatin in vaccines has been highly purified and hydrolyzed, so it is much smaller than that found in nature.
    • Thus, religious leaders believe it to be different enough that it does not break religious dietary laws. 
    • Religious leaders (from Judaism, Islam and Seventh-day Adventists) have stated that the benefits of receiving vaccines outweigh adherence to religious dietary laws.
  • The gelatin used in vaccines must be sourced from countries whose cattle are free of bovine spongiform encephalopathy (mad cow disease in cattle).
  • There are no reported cases of variant Creutzfeldt-Jakob disease (mad cow disease in humans) linked to bovine gelatin, despite tens of millions of vaccines manufactured using bovine-derived material.
Thimerosal is a mercury-based preservative used in vaccines produced in multi-dose vials. Preservatives prevent germs (bacteria and fungus) from growing in the vial after the first dose has been removed.
Thimerosal has been used safely in vaccines for a long time. Scientists have been studying the use of thimerosal in vaccines for many years. They haven’t found any evidence that thimerosal causes harm.
  • In the body, thimerosal is metabolized to ethylmercury and thiosalicylate. Ethylmercury is different from methylmercury (the type of mercury found in the environment that can cause mercury poisoning). Ethylmercury is broken down and excreted much more rapidly than methylmercury and is much less likely to accumulate in the body and cause harm. It has a half-life of seven days as opposed to 50 days for methylmercury.
  • Studies have shown that thimerosal, at the levels contained in vaccines, is easily eliminated from the body and does not cause neurological problems.
  • In Canada, thimerosal is only used in some influenza vaccines provided in multi-dose vials. The amount of thimerosal is not greater than 50 µg per 0.5 mL dose. 
  • Thimerosal has not been included in any routine childhood vaccines produced since 2001. It was removed as a precautionary measure to maintain public confidence in vaccines, not because there was evidence that thimerosal in vaccines was dangerous.
  • Studies have shown that the small amount of thimerosal used to preserve vaccines is safe.
  • The evidence is clear that thimerosal in vaccines does not cause autism.
  • The amount of mercury in a thimerosal-containing influenza vaccine does not exceed 25 µg/dose. This is about the same amount as is found in a six-ounce can of Canadian albacore tuna, which has no serving limits and is considered safe to eat.
Human fetal cells
Some vaccines are made by growing the vaccine viruses in human fetal cells. The fetal cells that are used to grow vaccine viruses were originally obtained from fetuses aborted decades ago. The fetuses were not aborted to make vaccines.  These same cells continually grow in the laboratory, and no new sources of fetal cells are used to make vaccines today. 
  • Fetal cells are used because viruses need to be grown in cells, and human cells are often better than animal cells at supporting the growth of human viruses. 
  • The vaccines themselves do not contain fetal cells or tissue. 
  • The purification process removes nearly all the cell components so that only trace amounts of DNA and protein may be present in the vaccine. 
  • Ethicists from the US National Catholic Bioethics Center concluded that the use of human cells in vaccine production was not contrary to their religious practices or beliefs. A statement from the Vatican says, “Parents have a serious obligation to protect their children from disease whenever possible, and in doing so, they are not signaling their approval for abortion.” 
  • The following vaccines used in Canada are made by growing the vaccine viruses in fetal cells:
    • Varicella (chickenpox) vaccines.
    • Hepatitis A vaccines (including Twinrix and the travel vaccine Vivaxim, which protects against typhoid and hepatitis A).
    • Rubella vaccines (given as measles, mumps, rubella (MMR) and measles, mumps, rubella, varicella (MMRV)).
    • One rabies vaccine (Imovax Rabies).
    • One shingles vaccine (Zostavax II).
    • There are 2 COVID-19 vaccines authorized for use in Canada that are made using fetal cells: the AstraZeneca/COVISHIELD vaccine and the Janssen (Johnson & Johnson) vaccine. Although fetal cells are not used to make the Moderna and Pfizer COVID-19 vaccines, they were used in the very early stages of development of these vaccines to test “proof of concept” (to test that the vaccines could work).
Animal cell lines
Animal cell cultures are used in the process of making certain vaccines, but the vaccines do not contain animal cells or tissue. 
  • They are used because the viruses needed to make some vaccines can only be grown in human or animal cells.
  • The purification process removes nearly all cell components so that only trace amounts of DNA and protein may be present in the vaccine.
  • Vero cells, derived from the kidney of an African green monkey in the 1960s, have been used to produce safe and effective vaccines for decades. 
Blood products
Human blood products are not typically found in vaccines. The exceptions to this are two rabies vaccines (Imovax® Rabies and RabAvert®) that contain albumin derived from human blood. 
Egg or chicken products
Some vaccines (e.g., influenza (flu), MMR, and MMRV) contain egg or chicken protein. 
  • These vaccines contain egg or chicken protein because the viruses used to make them are grown in eggs or cells isolated from chicken embryos. 
  • People with egg allergies can be safely immunized with these vaccines.
Trace amounts of antibiotics are present in some vaccines because they are used to prevent bacterial contamination during the manufacturing process. 
Some vaccines are made in yeast cells. The vaccines are purified to remove almost all of the yeast, but trace amounts of yeast protein may remain in the final product. 

Safety of vaccine ingredients

Vaccine ingredients have been carefully studied for a long time and are safe in the small amounts used. 
The ingredients in vaccines have not been proven to cause harm (disease or illness) in the small amounts used in vaccines, with the exception of allergic reactions in people with hypersensitivity to a specific ingredient. Before administering a vaccine, your health care provider will:
  • Ask you about any known allergies or previous reactions to vaccines.
  • Assess whether any given vaccine is not safe for you to receive. 
If you have an unexpected allergic reaction after receiving a vaccine, your health care provider will be able to recognize and treat it quickly.

Ingredients in specific vaccines

Part 1 of the Canadian Immunization Guide has a table that lists the ingredients in vaccines used in Canada. 
The Government of Canada website lists the ingredients in each COVID-19 vaccine. 
You can also find a list of vaccine ingredients in the vaccine's product monograph. Product monographs are available through Health Canada's Drug Product Database.