Vaccines Get New Scrutiny
Vaccinations are supersafe, but maybe not all at once, or for certain children
"It's one thing to take a risk [with a medication] if you actually have a disease, but taking a risk when the goal is prevention of a very rare disease is less tolerable," says Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania. Menactra, for example, protects against bacterial meningitis, which strikes about 1 in 100,000 people per year and kills about 1 in a million. But it also may cause Guillain-Barré syndrome, a temporary but severe paralysis triggered by an overactive immune system, in 1 to 2 teens per million who are vaccinated, according to Iskander.
New vaccines like Menactra and Gardasil pose unknown safety risks because, like any drug submitted for FDA approval, they only need to be tested in several thousand people. "These trials simply aren't big enough to detect rare events that only come to light after 1 million or more doses are distributed," says Iskander. The original vaccine against rotavirus, which causes severe diarrhea and dehydration in infants, was tested on fewer than 1,300 American infants before it was approved in 1998; a year later, after being given to 1.5 million babies, RotaShield was pulled from the market because 13 reported cases of severe intestinal blockages were attributed to the vaccine. The meningitis vaccine Menactra was studied in just over 7,500 people before it was approved in 2005 for adults and kids over age 11. It wasn't until last February, after 15 million doses had been administered, that the CDC announced a "small increased risk" of Guillain-Barré that needs to be studied further.
Hit or miss. The CDC's current system of detecting rare problems is hit or miss. Perhaps the crudest tool is the Vaccine Adverse Event Reporting system, which relies on doctors and patients to file a report if they suspect symptoms have been caused by a vaccine. Many problems filed with VAERS have nothing to do with vaccinations; real adverse events often go unreported. A better monitoring system, the agency's Vaccine Safety Datalink, regularly scans 5.5 million anonymous health records provided by managed care organizations to see whether new vaccines are associated with a spike in certain conditions. Still, even the Datalink database doesn't hold enough teens to definitively prove a causal link between Guillain-Barré and Menactra, says Harvard Medical School professor and vaccine researcher Richard Platt. He and his colleagues recently established a surveillance system that includes 50 million people and are using it to check for Menactra-related Guillain-Barré cases in more than 9 million young people ages 11 to 21. Platt expects to publish results sometime in 2009.
This larger surveillance system could also help determine whether there's a limit to the number of immunizations a baby can safely have at once. The Institute of Medicine concluded in 2002 that giving babies 20 shots against 11 diseases before age 2 did not raise the risk of juvenile diabetes (thought to be a result of an immune system in overdrive). But the IOM decided there wasn't enough evidence to prove or disprove an increased risk of allergies and asthma. Efforts are underway in Congress to fund a well-designed study comparing vaccinated kids against those who remain unvaccinated to see if there are differences in autism rates.
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