Vaccine Additives and Preservatives

Parents holding baby girl while pediatrician prepares vaccination
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Vaccines may contain "live viruses, killed viruses, purified viral proteins, inactivated bacterial toxins or bacterial polysaccharides," which is how our bodies know how to develop antibodies and an immune response against the infection that the vaccine is supposed to protect us against.

Vaccines also contain additives and preservatives.


The most well-known preservative in vaccines is thimerosal, which some people thought could possibly be linked to autism.

No link to autism or other conditions have ever found, but because of concerns that thimerosal could be harmful and since alternatives to thimerosal were available, the FDA states that "thimerosal has been removed from or reduced to trace amounts in all vaccines routinely recommended for children 6 years of age and younger, with the exception of the inactivated influenza vaccine."

While multidose vials of flu vaccine with thimerosal are still being made, at least 105 million doses of flu vaccine being supplied this year are either thimerosal-free or preservative free (with a trace amount of thimerosal).

It is important to note that even when the FDA began to review the presence of thimerosal in vaccines in 1998, it was because the EPA had just revised their mercury intake guidelines for oral methylmercury, and that:

  • Thimerosal is only about 50% ethylmercury (not the same as methylmercury)
  • The EPA guidelines were not set at a toxic level and included a 10-fold safety factor
  • The EPA guidelines were assuming a cumulative dose of methylmercury over time, like if you drank contaminated water every day
  • Only three vaccines were being made with thimerosal—hepatitis B and some versions of Hib and DTaP

Still, some parents are worried that chemicals, additives, and preservatives in vaccines are harmful, which has prompted groups such as the Green Vaccine initiative to call for "safer" vaccines. These anti-vax initiatives simply push myths that scare people about vaccines, though.

Additives and Preservatives

Although mercury has been removed from most vaccines, vaccines may still contain aluminum, formaldehyde, human serum albumin, gelatin, antibiotics, and yeast proteins.


Some, such as aluminum salts, help the vaccine to work better. Other additives, such as human serum albumin, help stabilize live viruses in the vaccine. And others, such as formaldehyde, antibiotics, egg proteins and yeast proteins, are left over in residual amounts from the way that vaccines are made.

Formaldehyde? Why is formaldehyde in the vaccines that we give our children?

Formaldehyde is present in some of the vaccines on the childhood immunization schedule, including the flu shot, polio vaccine, and DTaP vaccine, because it works to eliminate the harmful effects of these bacterial toxins and makes the viruses unable to replicate or reproduce themselves. The very small amount of formaldehyde that is left over in the vaccines that are given to kids is less than the amount naturally found in children and much less than that amount safely given to animals in research studies.

What about antifreeze? Don't vaccines have antifreeze in them?

Not really. Some vaccines do contain the additive 2-phenoxyethanol, which is an organic chemical compound, but it is not the same as antifreeze (ethylene glycol). 2-Phenoxyethanol is also a glycol ether and doesn't sound much better than antifreeze, so why is it in vaccines? It is a safe preservative that can help prevent bacterial and fungal contamination of the vaccine. It is also used as a stabilizer in some vaccines.

What about propylene glycol? Isn't that the same as antifreeze? Propylene glycol is a safer component of antifreeze but isn't in vaccines either.


Unfortunately, vaccine additives do sometimes cause reactions, with the most common being allergic reactions to gelatin, the antibiotic neomycin, and eggs (flu shot and yellow fever vaccine).

Still, these reactions are very rare.

According to the AAP, "Parents should be reassured that quantities of mercury, aluminum, and formaldehyde contained in vaccines are likely to be harmless on the basis of exposure studies in humans or experimental studies in animals."

And keep in mind that it was much more common for children to get sick from contaminated vaccines before the use of preservatives. Also, of course, additives that have helped vaccines work better have helped prevent millions of vaccine-preventable illnesses and deaths.

The Dose Makes the Poison

Paracelsus once said that "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison."

And 500 years later, Dr. Paul Offit explained it again, in response to misinformation by Dr. Bob Sears, saying that "By creating the notion of zero tolerance, Sears fails to educate his readers that the dose makes the poison, that it is the amount of a potential toxin and not its mere presence that counts."

So the mere presence of formaldehyde, neomycin, streptomycin, and aluminum, etc., in vaccines doesn't make them toxins.

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Article Sources
  • Centers for Disease Control and Prevention. Ingredients of Vaccines - Fact Sheet.

  • Offit, Paul A. MD. Addressing Parents' Concerns: Do Vaccines Contain Harmful Preservatives, Adjuvants, Additives, or Residuals? Pediatrics. Vol. 112 No. 6 December 2003, pp. 1394-1397.

  • Offit, Paul A. MD. The Problem With Dr. Bob's Alternative Vaccine Schedule. Pediatrics. Vol. 123 No. 1 January 1, 2009. pp. e164 -e169.

  • Parker, Sarah K MD. Thimerosal-Containing Vaccines and Autistic Spectrum Disorder: A Critical Review of Published Original Data. Pediatrics Vol. 114 No. 3 September 1, 2004 pp. 793-804.

  • Plotkin: Vaccines, 5th ed.