Can the ingredients in vaccines hurt my baby?

Short Answer

Vaccines are not perfect in safety or effectiveness, but overall they are considered to be among the greatest achievements in public health, lowering the rate of infectious illness to a fraction of what it was a century ago.

Just like prescribed or over-the-counter medication, there is a small risk of side effects and negative interactions due to allergies or rare sensitivities. Make sure to discuss any known allergies with your child’s doctor. Vaccines undergo rigorous and thorough testing for safety and efficacy over the course of years before they are licensed for use in the public, and are continually monitored by doctors, scientists, and the public after they’re released.


Vaccines are rigorously tested for safety and efficacy, and are only released to the pubic after they have been thoroughly studied in clinical trials, as are all medications and pharmaceuticals approved by the U.S. Food and Drug Administration (FDA).

Vaccines contain either a weakened or killed version of an infectious microbe (virus or bacteria). Tiny amounts of other ingredients are added to some vaccines to increase the efficacy and decrease the possibility of contamination. These ingredients are present in very low amounts and are not considered toxic for children or adults. However, in rare instances, individuals can be sensitive or allergic to these ingredients.

In July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal (ethylmercury) levels in vaccines should be reduced or eliminated as a precautionary measure. This step was undertaken in part to achieve the broader goal of reducing exposure to mercury wherever feasible and, in part, to avoid a false perception of risk from vaccines that could result in parents avoiding life-saving vaccines. It is important to note that data has shown that autism levels continue to rise despite the removal of thimerosal. During the past several years, a series of biological and epidemiological studies have examined thimerosal and found no evidence that the preservative causes harm to infants or children.