How Safe Are Vaccines?

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The Autism Riddle
More than any other issue, the question of autism has fueled the battle over vaccines. Since the 1980s, the number of vaccinations children receive has doubled, and in that same time, autism diagnoses have soared threefold. In 1998, British gastroenterologist Dr. Andrew Wakefield of London's Royal Free Hospital published a paper in the journal the Lancet in which he reported on a dozen young patients who were suffering from both autism-like developmental disorders and intestinal symptoms that included inflammation, pain and bloating. Eight of the kids began exhibiting signs of autism days after receiving the MMR vaccine against measles, mumps and rubella. While Wakefield and his co-authors were careful not to suggest that these cases proved a connection between vaccines and autism, they did imply, provocatively, that exposure to the measles virus could be a contributing factor to the children's autism. Wakefield later went on to speculate that virus from the vaccine led to inflammation in the gut that affected the brain development of the children.

Like the initial tremor that triggers a massive earthquake, Wakefield's theories resonated throughout the autism community, where vaccines had been regarded with suspicion for another reason as well. Ever since the 1930s, a mercury compound known as thimerosal had been included in some vaccines—though not the measles inoculation—as a preservative to keep them free of fungi and bacteria. Thimerosal can do serious damage to brain tissue, especially in children, whose brains are still developing. It was perhaps inevitable that parents would make a connection between the chemical and autism, since symptoms typically appear around age 2, by which time babies have already received a fair number of vaccines. That link could be merely temporal, of course; babies also get their first teeth after they get their first vaccines, but that doesn't mean one causes the other.

In 2001, however, a U.S. Food and Drug Administration study revealed that a 6-month-old receiving the recommended complement of childhood vaccinations was exposed to total levels of vaccine-based mercury twice as high as the amount the epa considers safe in a diet that includes fish. By the end of that year, thimerosal-free formulations of the five inoculations that included it—hepatitis B, diphtheria, tetanus and pertussis and some versions of Haemophilus influenzae type b (Hib)—had replaced the older versions. The result was a drop in mercury exposure in fully immunized 6-month-old babies from 187.5 micrograms to just trace amounts still found in some flu vaccines. Yet there's been no effect on autism rates. In the seven years since the cleaned-up vaccines were introduced, new cases of autism continue to climb, reaching a rate of 1 in every 150 8-year-olds today. That trend suggests that other factors, including heightened awareness of the condition and possible genetic anomalies or environmental exposures, are behind the climbing rates. What's more, in the decade since Wakefield's watershed paper, 10 of its 13 authors have retracted their hypothesis, admitting that the study did not produce solid enough evidence to support a connection between the measles virus in the MMR vaccine and autism.

But the damage had been done. Parents, already uneasy about immunizations, now felt betrayed by government health authorities and a vaccine industry that simply kept the shots coming, with today's kids receiving up to 28 injections for 14 diseases, more than double the number of shots required in the 1970s. "There is no doubt in my mind that my child's first cause of autism is the mercury in vaccines," says Ginny DeLeo, a New York science teacher whose son Evan, born in 1993, was developing normally until he was a year old. The day the boy received his fourth dose of Hib vaccine, DeLeo had to rush him to the hospital with tremors and a 104 deg F (40 deg C) fever, which later led to seizures. Evan recovered, and several months later he received the first of two MMR shots. Within months, he stopped talking, and autism was diagnosed.

So, is there a link? In 2003, a 15-person committee impaneled by the CDC and the National Institutes of Health analyzed the available studies on thimerosal and its possible connections to autism and concluded that there was no scientific evidence to support the link. In a further show of confidence, the committee noted that it did "not consider a significant investment in studies of the theoretical vaccine-autism connection to be useful." Instead, the panel recommended that studies focus on less explored genetic or biological explanations for the disease.

There is also little evidence to support the claim made by antivaccine activists that the battery of shots kids receive can damage the immune system rather than strengthen it. Experts stress that it's not the number of inoculations that matters but the number of immune-stimulating antigens—or proteins—in them. Thanks to a better understanding of which viral or bacterial proteins are best at activating the immune system, that number has plummeted. The original smallpox injection alone packed 200 different immune-alerting antigens in a single shot. Today there are only 150 antigens in all 15 or so shots babies get before they are 6 months old. "The notion that too many vaccines can overwhelm the immune system is just not based on good science," says Dr. Paul Offit, chief of infectious diseases at Children's Hospital in Philadelphia.