Weighing The Risks
That doesn't mean that vaccines aren't capable of causing adverse effects beyond a sore arm and a slight fever. In 1986, the government created the National Vaccine Injury Compensation Program to reimburse families whose children had serious side effects, and it has awarded nearly $2 billion on 2,398 claims. But most doctors say that the odds of experiencing a vaccine-related injury are greatly outweighed by the dangers of catching a vaccine-preventable disease. The measles vaccine, for instance, can cause a temporary reduction in platelets (which control bleeding after an injury) in 1 in 30,000 children, but 1 in 2,000 will die if they get measles itself. The DTaP vaccine can cause seizures or a temporary "shocklike" state in 1 in 14,000 people, and acute encephalitis (brain swelling) in 11 in 1 million. But the diseases it prevents -- diphtheria, tetanus, and pertussis -- are fatal in 1 in 20 cases, 1 in 10 cases, and 1 in 1,500 cases, respectively.
If the FDA determines that a vaccine poses a real risk to more than a tiny percentage of children, the agency won't let it be used. "Before a new vaccine is approved, it goes through a prospective, placebo-controlled trial involving tens of thousands of children," says Dr. Offit, who was a cocreator of RotaTeq, one of two current rotavirus gastroenteritis vaccines. Once a vaccine is in use, side-effect reports are analyzed by the Vaccine Safety Datalink, a program that collects patient information from managed-care organizations. In 2001, government scientists concluded that Wyeth's Rotashield, an earlier vaccine against rotavirus, could cause one extra case of bowel obstruction for every 10,000 babies who were immunized each year, and they halted its use in the U.S. Sometimes vaccines are pulled from shelves as a precaution: In 2007, certain lots of Merck's Hib vaccine were recalled after the company found bacteria on manufacturing equipment, even though the vaccines themselves tested negative for contamination.