A: The Food and Drug Administration (FDA) requires rigorous testing of vaccine manufacturers, and each vaccine undergoes years of testing before it's ever made available to the public. Moreover, when a vaccine does go on the market, the Centers for Disease Control and Prevention (CDC) and the FDA continue to track reactions. About 10 years ago, for example, a vaccine called the Rotashield was introduced to protect against rotavirus, a stomach bug that causes severe diarrhea and vomiting in infants. Just a few months later, a rare, but potentially life-threatening side effect was discovered: Of the one million children who were vaccinated, about one in 10,000 developed severe intestinal blockage. The FDA immediately pulled the Rotashield off the market. (Now, much safer versions of rotavirus vaccines are available.) Of course, no vaccine is absolutely 100 percent safe or effective for every single child, but serious reactions are extremely rare. In most cases, the benefits of receiving a vaccine far outweigh the risks of contracting the disease itself. If you have questions about specific vaccinations or their side effects, you should talk to your pediatrician. --Maureen Connolly
Originally published in American Baby magazine, February 2004. Updated 2009.