Vaccine ingredients

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Vaccines contain small amounts of specific ingredients, all of which play necessary and important roles during vaccine production.

All of these ingredients are safe in the amounts used in vaccines. 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?

All vaccine ingredients serve a specific purpose in either making the vaccine or ensuring that the vaccine is safe and effective (works well). This section describes some of the vaccine ingredients people often ask questions about, including why they are in vaccines and their safety. 
  • Antigens are considered the active ingredients in vaccines because they are what cause the body’s immune system to respond (they teach the body’s immune system to recognize and attack the real germ). 
  • Antigens are either killed, weakened (‘attenuated’), or synthetically manufactured versions of the disease-causing germ or parts of the germ. 
  • Vaccines contain only a tiny fraction of the antigens that people encounter in their environment every day.
  • Vaccines do not cause disease in people with healthy immune systems because the germs are either weakened or killed.  However, live vaccines are not given to people with very weak immune systems as they may develop the disease the vaccine is meant to protect against. Learn more about the different types of vaccines here
  • 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 and is 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 record of safety. 
  • About half of the aluminum from vaccines is eliminated from the body in less than 24 hours, and 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 that can be present in vaccines. 
  • Health Canada follows standards set by the World Health Organization and allows for no more than 1.25 mg/dose as a safe level in vaccines

  • Formaldehyde is used during the manufacturing process of some vaccines to kill viruses or inactivate bacterial toxins.
  • The vaccines are purified to remove almost all the formaldehyde and 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. 
  • Gelatin is used in some vaccines as a stabilizer. 
  • Stabilizers help protect 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.
  • Gelatin in vaccines is sourced from cows and pigs.
  • Because some religious groups, such as Jewish people, Muslims, and Seventh Day Adventists, follow dietary rules that prohibit pork products, some parents are concerned about using vaccines that contain gelatin. However, all 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 these groups believe 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.
  • 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 cells 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 of the 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., the influenza, MMR, and MMRV vaccines) contain egg or chicken protein. 
  • Egg or chicken protein is present in these vaccines because the viruses used to make them are grown in eggs or in 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. 

Are the ingredients in vaccines safe?

The ingredients in vaccines have been carefully studied for a long time, and are safe in the small amounts used in vaccines. 
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 and will 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.

Where can I find a list of the ingredients in each vaccine?

The Canadian Immunization Guide has a table that lists the ingredients for vaccines used in Canada. 
The ingredients for COVID-19 vaccines are also available. They can be found on this page of the Government of Canada website (click on the vaccine name). 
A list of ingredients in each vaccine can also be found in the vaccine’s product monograph available through Health Canada's Drug Product Database.
These pages do not list ingredient amounts, and it is important to remember that ingredients in vaccines are in small amounts and are safe in the amounts used. 
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  • Children’s Hospital of Philadelphia. Vaccine ingredients: What you should know [Internet]. Philadelphia (PA): Children’s Hospital of Philadelphia; 2020 [cited 2021 Mar 4] 2 p. Available from:
  • Children’s Hospital of Philadelphia. Aluminum in vaccines: What you should know [Internet]. Philadelphia (PA): Children’s Hospital of Philadelphia; 2014 [cited 2021 Mar 4] Aluminum in vaccines: What you should know. Vaccine safety: Immune system and health. 2021 Jan 26 [cited 2021 Mar 4]. 2 p. Available from: data/files/pdfs/vaccine-education-center-aluminum.pdf 
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  • National Advisory Committee on Immunization. Canadian Immunization Guide [Internet]. Evergreen ed. Ottawa (ON). Public Health Agency of Canada. 2012 [updated 2021 Jan 8]. Part 2 – Vaccine safety: Contraindications, precautions and concerns; [cited 2021 Mar 4]. Available from: publications/healthy-living/canadian-immunization-guide-part-2-vaccine-safety/page-3-contraindicationsprecautions-concerns.html 
  • Canadian Albacore Tuna [Internet]. Victoria (BC): Canadian Highly Migratory Species Foundation; c2015. The facts about mercury 2015 Jul 24 [cited 2021 Mar 4]. Available from: 
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Date last reviewed: 
Thursday, Jul 15, 2021