Vaccine FAQ: Autism, Immunity, Mercury, Safety, SIDS

Today, children routinely receive 21 immunizations before they enter kindergarten — more than double what they received even a decade ago. Vaccine fears are present on social media, in parenting circles, and within community groups. This FAQ addresses parents' fears.

How Is Vaccine Safety Monitored?

Like antibiotics, vaccines have prevented unfathomable suffering, but some parents may worry about the potential side effects of giving them to their children. Immunization safety and monitoring is an important conversation. The Centers for Disease Control and Prevention (CDC) states “To ensure the continued success of vaccines in the United States, it’s crucial to make sure that vaccines are safe.” Before vaccines are approved by the FDA, they are thoroughly tested, and safety is always a priority during the development and approval process. And just because a vaccine is FDA approved and licensed doesn’t mean scientists are done studying it.  The CDC uses a variety of systems for continued monitoring, including the vaccine adverse event reporting system (VAERS).  The system allows anyone, clinician or patient, to report any undue side effects from a vaccine. This information is used to detect any concerns or trends requiring further investigation or intervention.  The current vaccine recommendations represent the best information available and are updated at least once a year. My hope is that open conversation about vaccines strengthens parents’ confidence in vaccines for their children.

Do Vaccines Increase SIDS?

Babies receive multiple vaccines between 2-4 months, which are also the peak age for SIDS. However, multiple reliable studies have failed to show any relationship between SIDS and childhood immunizations.  Research has shown that since the “1994 Back to Sleep Campaign” (in which it is recommended that healthy babies sleep on their backs), the incidence of SIDS has dramatically decreased.  During these last two decades, the number of baby vaccines has actually increased, providing strong evidence that immunizations and SIDS are unrelated. 

Do Vaccines Weaken the Immune System?

Babies get so many shots these days. About a quarter of parents are concerned that the sheer number of immunizations might overwhelm, weaken, or use up a baby’s immature immune system. Evidence published in multiple studies suggest that the opposite is true. 

By conservative estimates, their sturdy immune systems are built to be able to respond to as many as 10,000 foreign proteins by making antibodies to them. The study explains that if a baby were to receive all 12 available immunizations at once, this would occupy only a tiny fraction of the immune system — and that part would be quickly replenished.

Compared with the huge exposure children normally have to the germs in their environment (and in their own bodies) a vaccine is quite small. And even though the number of vaccines children receive has increased recently, the number of proteins in these vaccines has dropped.

One vaccine, the smallpox vaccine, used to contain 200 proteins. Today’s recommended vaccinations contain only around 130 proteins combined. And these help to prepare your child’s immune system to respond to its most important threats.  The risks of going unvaccinated far outweigh any perceived risk of the vaccine itself. 

Questions about Mercury?

Thimerosal (a form of mercury) was taken out of childhood vaccines in 2001.  Many vaccines never even contained thimerosal, and it is only used now in multi-dose vials as a preservative to prevent the growth of bacteria in the vaccines.  There is no evidence that the small amount of thimerosal used as a preservative causes anything more than slight redness at the injection site.  A single-use vial does not contain thimerosal, and all vaccines for children under 6 years of age are offered as thimerosal-free. 

Vaccines and Autism?

There is no evidence that childhood immunizations cause or contribute to the development of autism. Even after thimerosal was removed from childhood vaccines autism rates have continued to increase, which would not be expected if thimerosal was contributing to the development. 

Resources and References

CDC information- thimerosal and vaccines

Glanz JM, Newcomer SR, Daley MF, et al. Association between estimated cumulative vaccine antigen exposure through the first 23 months of life and non-accine-targeted infections from 24 through 47 months of age. JAMA 2018;319(9):906–913.

Farrington CP, et al. MMR and autism: further evidence against a causal association. Vaccine. 2001;19(27):3632-5.

Last medical review on: April 06, 2021
About the Author
Photo of Alan Greene MD
Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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