The Truth About Vaccine Ingredients

Photo courtesy of the CDC

As parents, we recognize the importance of reading labels. I’m just as guilty as the next person: Follow me around the grocery store during my weekly shopping trip, and you’ll see that I’m definitely one of those people who stands in the aisles reading labels of every packaged food I buy, and I quickly reject anything that has a laundry list of ingredients with a lot of unfamiliar, unpronounceable items.

But some people are now trying to apply that same “logic” to vaccines.

I can understand the desire to be thorough about vaccine ingredients, because this is something we’re putting into our own bodies and into the bodies of our children. But truth is, the unfamiliar (and often hard-to-pronounce) ingredients in vaccines are typically the very things that make those vaccines safe. I for one actually want a vaccine with the ingredients that keep the vials from getting contaminated with germs; as well as ingredients that help ensure the vaccine stays safe yet potent and uncontaminated while being stored. Before scientists figured out how to safely store vaccines, there were tragic consequences.

But let’s face it – the list of ingredients can sound a bit daunting to your average parent who doesn’t have a PhD in Biochemistry. Like many of the foods we eat, small amounts of chemicals may be added to the vaccine's formula to preserve or improve its effectiveness and keep it sterile.

The U.S. Food and Drug Administration (FDA) does an excellent job explaining the reason for preservatives here:

“We need to answer two questions — what are preservatives, and why are they used in vaccines. For our purposes, preservatives may be defined as compounds that kill or prevent the growth of microorganisms, particularly bacteria and fungi. They are used in vaccines to prevent microbial growth in the event that the vaccine is accidentally contaminated, as might occur with repeated puncture of multi-dose vials. In some cases, preservatives are added during manufacture to prevent microbial growth.”

I don’t know about you, but microbial growth seems like a good thing to prevent.

So now let’s take a minute to look into some of these specific ingredients you’ve heard about in relation to vaccines. Keep in mind: Sometimes a child may be sensitive to one of the components of a vaccine, and an allergic reaction may result. For this reason, you should discuss any allergies your child may have with your health care provider.

Thimerosal and Mercury

Once upon a time, childhood vaccinations contained a preservative called thimerosal.  The substance of concern in thimerosal, of course, is mercury.  However, it’s important to understand a key distinction when it comes to the type of mercury we are talking about.

Mercury is a naturally occurring element found in the earth’s crust, air, soil and water.  Methylmercury is formed in the environment when mercury metal is present. Methylmercury makes its way through the food chain in fish, animals and humans. At high levels, it can be toxic to people.  Also important to note: Babies are exposed to methylmercury in milk, including breast milk. An infant who is exclusively breast-fed will ingest more than twice the quantity of mercury than was ever contained in vaccines. Another way to look at it: the mercury you’ll consume in a can of tuna is 3X as much as in a flu vaccine.

Ethylmercury is formed when the body breaks down thimerosal. Low-level ethylmercury exposures from vaccines are very different from long-term methylmercury exposures because ethylmercury is broken down by the body differently and clears quickly.

Even though there have been numerous studies concluding the safety of thimerosal, in July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure.  Since 2001, thimerosal has not been used as a preservative in routinely recommended childhood vaccines.

The one exception is the influenza vaccine. The injectable flu vaccine is available in two ways: multidose vials or single dose. There is a very small amount of thimerosal in the multi-dose vials to ensure that no bacteria will grow in the vaccine. Single dose, pediatric formulation for 6 mos-3 years and FluMist are preservative free. 

In other words, YOUR young baby will not be getting vaccines that contain mercury (thimerosal) as a preservative.

For more information about mercury and thimerosal, click here.

Most parents have questions about thimerosal. But if you have questions about additional vaccine ingredients, click here for our post on others and common myths we hear. 

This article was written by Heidi Parker, Executive Director of Immunize Nevada, Lynnette Bellin, Director of Strategic Communications for Immunize Nevada and Mikalee Byerman, Director of Audience Engagement at Estipona Group.  It was reviewed for medical accuracy by Dr Shaji Mathew, MD, PhD, FAAP of Summit Pediatrics.  

Immunize Nevada

Immunize Nevada, an award winning 501c3 non profit, is widely recognized as Nevada’s trusted resource for immunizations and community health for all ages by fostering education and statewide collaboration.


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