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Thimerosal in vaccines

Learn about the safe use of this ingredient in some vaccines.

About thimerosal

Thimerosal is used as a preservative in some vaccines. It keeps the vaccine safe for a longer time, and only very small amounts are used. Thimerosal is safe to use to preserve vaccines.

Thimerosal breaks down into ethylmercury. It leaves your body quickly when you have a bowel movement (poop). Ethylmercury does not build up in your body and is not the same as other types of mercury, such as:

  • methylmercury: found in sword fish, tuna, king mackerel, and shark
  • phenylmercury: a chemical used to kill fungus

In 2004, the National Academy of Medicine Immunization Safety Review Committee found that there is no link between thimerosal and autism.

Thimerosal in vaccines

Thimerosal keeps vaccines safe by stopping bacteria and fungi from growing inside the vial of a vaccine. If a vaccine becomes contaminated (unsafe), it could cause serious infections in people who get it.

Thimerosal is also used to kill viruses or bacteria in some vaccines.

Vaccines in Alberta

In Alberta, only a few vaccines have thimerosal.

Some vials of influenza vaccine have small amounts of thimerosal. Other routine childhood vaccines have not had thimerosal since 1994.

Live vaccines, such as MMR vaccine and varicella vaccine, have never had thimerosal as an ingredient.

Autism and brain development

In 2004, the National Academy of Medicine (formerly the Institute of Medicine) Immunization Safety Review Committee found that there is no link between thimerosal and autism.

Since then, studies have shown no link between thimerosal and brain development disorders.

The National Advisory Committee on Immunization says there is no safety reason to stop using vaccines with thimerosal.

Learn more

If you have questions about thimerosal, vaccine ingredients, or vaccine safety, talk to a public health nurse, your doctor, or your pharmacist.

Current as of: June 30, 2023
Author: Provincial Immunization Program, Alberta Health Services
Our work takes place on historical and contemporary Indigenous lands, including the territories of Treaty 6, Treaty 7 & Treaty 8 and the homeland of the Métis Nation of Alberta and 8 Métis Settlements. We also acknowledge the many Indigenous communities that have been forged in urban centres across Alberta.