Many Americans senselessly fear harmless traces of mercury in the fish they eat, but the flip side of the Great Mercury Scare has been the presence of thimerosal (a preservative that contains mercury) in some children’s vaccines. In landmark research appearing in today’s New England Journal of Medicine, researchers from the Centers for Disease Control and Prevention found that mercury in vaccines has no effect whatsoever on children’s brain functioning.

This episode is one of the most interesting failures of the omnipresent “Precautionary Principle.” Countless parents actually stopped having their kids vaccinated, believing that health risks related to mercury (including autism, a claim trumpeted repeatedly by über environmentalist Robert F. Kennedy Jr.) were worth avoiding at all costs. Those costs, however, included the very real risk of being hospitalized (or dying) from the flu or some other avoidable infection.
In a New England Journal of Medicine opinion piece today, Children’s Hospital of Philadelphia Infectious Diseases chief Dr. Paul Offit writes: 

Although the precautionary principle assumes that there is no harm in exercising caution, the alarm caused by the removal of thimerosal from vaccines has been quite harmful … the thimerosal controversy should stand as a cautionary tale of how not to communicate theoretical risks to the public; otherwise, the lesson inherent in the collateral damage caused by its precipitous removal will remain unlearned.
It’s worth remembering that there has been similar “collateral damage” in our irrational (mercury-related) fear of fish. Americans who go cold-turkey on tuna and other seafood risk losing the health benefits of Omega-3 fatty acids. And since evidence keeps pouring in that these very real health benefits far outweigh the theoretical risks from mercury (see here, here, here, here, and here), adding the Precautionary Principle to our dinner plates looks like a risk not worth taking.