A New England Journal of Medicine study has added another brick to the wall of evidence closing out a link between vaccines and autism and other brain disorders. Unfortunately, the public relations effect of the study will be muted because the anti-mercury activists who helped plan it withdrew their support when the results displeased them.
The study, released today, did not specifically address a link between vaccines and autism.
Rather, the scientists, led by the Centers for Disease Control, carried out a battery of neuropsychological tests on 1,047 7- to 10-year-old children who as infants had received various dosages of thimerosal. In 1999, the government asked drug companies to remove thimerosal from three pediatric vaccines that contained it. The active ingredient of thimerosal, a preservative, is ethyl mercury, a neurotoxin at high doses.
The study conducted a total of 378 different statistical tests with the data, based on 42 measurements of things like attention span, fine motor skills, tics and IQ. The authors found no impact of thimerosal in 359 of these data points, but found statistically significant results for 19 measures. About half of the latter showed that thimerosal exerted a positive effect, the other half potential harm. For example, males babies seemed to be more likely to have tics the more thimerosal they ingested. They also seemed to have better verbal skills.
The usual scientific explanation for such results is that they are artifacts of chance. Indeed, in any study with this many variables, scientists are certain to find some statistically significant results, just as a person flipping 378 different coins repeatedly would be certain to have a "significant" excess of either heads or tails for a few of the coins.
One potential concern in the study was the finding of tics, although the rate wasn't drastically higher in the high-thimerosal group. As the paper's lead author, William Thompson, explained to journalists, children of this age frequently experience "tics" that are transient and of no significance--repetitive clearing of the throat, say, or drumming of fingers. The neurologists who conducted the tests registered behaviors and mental capacities according to protocol, and irrespective of the clinical significance in a given child.
Naturally, the so-called Mercury Militia are having none of it. For them, this is yet another incidence of bad faith by the CDC.
SafeMinds and other activist groups have long accused the CDC of hiding vaccine safety problems. In response to those claims, which are backed by members of Congress who apparently share SafeMinds' belief, the CDC and other government agencies have invited activists to participate in research, in order to clarify that government scientists are not evil conmen but rather in most cases are endeavoring to find the truth.
Sallie Bernard, a New Jersey businesswoman and leader of SafeMinds (a group that alleges vaccines are responsible for an epidemic of autism) was on the external board that helped design the Journal study. But Bernard, in a statement released by SafeMinds, charged that the study "draws a misleading conclusion," a comment she backs with various complaints about the study's methodology, size and the wording of its abstract. Bernard, according to Thompson, withdrew her support for the study around the time its final draft was circulating.
Earlier in September, Bernard's group released a statement urging parents to make sure their children were not vaccinated with thimerosal-containing flu shots--the last remaining pediatric vaccines that sometimes contain the preservative.
This statement came at a particularly bad time for public health officials who are trying to increase flu vaccination levels among children this fall. A study in this week's Lancet Infectious Diseases showed, as has previous work, that campaigns to vaccinate the elderly against the flu are not very effective, because the old have immune systems that frequently don't respond to the killed flu virus vaccine. For this reason, the CDC has been trying to boost flu vaccination of the young to reduce the number of human vectors carrying the virus to the elderly. Flu can be an innocuous disease, but in the sick and old it can kill, alone or in combination with bacterial infections.
Despite the wealth of data showing that vaccines do not cause autism, many parents continue to believe the theory. Jenny McCarthy, an ex-Playboy Bunny and TV personage, has been making the rounds of the media this week (Oprah, ABC, People magazine) to promote her book, in which she claims that her child was made autistic by vaccines but was "recovered" through alternative therapies.
A large CDC study comparing thimerosal exposure rates in autistic and non-autistic kids is due out around this time next year, as is an Italian study of the question. The data will probably duplicate the many previous studies that have shown no effect. The dogs may bark but the caravan moves on. Or is it the other way around?