A Breakdown of Ingredients in Childhood Vaccines

Everything is in there for a reason.

ByABC News
February 10, 2015, 12:02 PM

— -- Parents who express misgivings about childhood vaccines are often responding to misinformation about what vaccines contain, experts say.

Dr. Frank Esper, an infectious disease doctor with the UH Rainbow Babies and Children's Hospital in Cleveland, stressed that each vaccine component is there for a reason and has been thoroughly tested for stability, safety and effectiveness.

“Nothing is thrown in there randomly,” he explained. “And everything is present in small amounts.”

Here, a Centers for Disease Control and Prevention breakdown of the most common vaccine ingredients and why they’ve been added.

Live Virus

The MMR and some other vaccines do contain live virus, but Esper said they have essentially been neutered in the lab by chopping out the genes that cause dangerous infection. They’re included so the body learns what the real virus looks like and can mount an immuno-response against it.


Found in gel or salt form, a minuscule amount of this metal is added to vaccines as “adjuvant,” meaning it helps promote a quicker, more potent immune response to the vaccine. Esper said this ingredient has tested well in numerous safety trials.


A tiny amount of this preservative added into a vaccine kills unwanted viruses and bacteria that might contaminate the vaccine during production. Most formaldehyde is removed from the vaccine before it is packaged, according to both the CDC and the Food and Drug Administration.

Thimerosal and Mercury

It is true that mercury is toxic in high doses. But the mercury-containing preservative thimerosal was present in vaccines in smaller amounts than naturally occur in water or soil to prevent contamination and bacterial growth, Esper pointed out. In any case this is a moot point: The compound was removed from virtually all childhood vaccines more than a decade ago.

Other Ingredients

Some vaccines contain antibiotics to prevent contamination or monosodium glutamate (MSG) to protect against light, heat and humidity. Some flu and yellow fever vaccines also contain egg proteins as part of the preparation process and should be safe for anyone who can eat eggs.