The percentage of American children who receive childhood vaccinations is dropping. Experts say that vaccine-resisters are more likely to be highly educated and well off financially. What has spooked them? Their chief fear is that vaccinations may trigger autism, a neurological disorder that typically appears before a child reaches the age of three. Such children suffer language and communication deficits, withdraw from social contacts, and react intensely to changes in the immediate environment.
Many parents of autistic children fervently believe that the measles-mumps-rubella (MMR) triple vaccine causes autism. Autistic symptoms make their appearance just about at the time that most children are vaccinated. The typical story is that little Johnny was fine until a couple of weeks after he was injected. However, most research suggests that parents are confusing correlation with causation—the symptoms of autism just happen to emerge at the about the same time as recommended vaccinations are given. It's a coincidence, not a cause. Public health experts worry that many parents are wrongly discounting the dangers that infectious diseases pose for their children because many have never seen a child afflicted with polio or whooping cough.
The MMR/autism hypothesis took off in 1998 with the publication of a study of 12 autistic children by Canadian gastroenterologist Andrew Wakefield at the Royal Free Hospital in London. Wakefield's study, appearing in the prestigious British medical journal The Lancet, found traces of the measles virus in the guts of the children he tested; Wakefield concluded that these traces derived from the MMR vaccination. The study noted that the onset of eight of the children's developmental disorders occurred shortly after they had received the MMR vaccine.
As a precaution, Wakefield suggested that children be vaccinated for each disease separately rather than with the combination vaccine. The MMR/autism connection was boosted by a report published in 2001 in the journal Medical Hypotheses by autism activist Sallie Bernard. Bernard argued that the mercury in the vaccine preservative thimerosal was "a novel form of mercury poisoning" that was responsible for autism. In June 2005, Robert F. Kennedy Jr. fueled the controversy with a sensational article in Rolling Stone and Salon that claimed there is a massive government cover-up of the dangers of MMR vaccines. Kennedy quoted school nurse Patti White who told the House Government Reform Committee in 1999. "Vaccines are supposed to be making us healthier; however, in twenty-five years of nursing I have never seen so many damaged, sick kids. Something very, very wrong is happening to our children."
Fortunately, years of subsequent research have not found an association between MMR vaccination and autism. In 2004, the National Academy of Sciences issued a report that concluded that "neither the mercury-based vaccine preservative thimerosal nor the measles-mumps-rubella (MMR) vaccine are associated with autism." In 2005, a comprehensive review of MMR of 31 studies by the non-profit authoritative medical collaboration, the Cochrane Library, found "no credible evidence behind claims of harm from the MMR vaccination."
These conclusions have been bolstered by other research. In 1993, Japan stopped using the MMR vaccine and began vaccinating for each disease separately. A study published last year found that autism rates continued to climb from 48 to 86 cases per 10,000 before MMR vaccination was halted to 97 to 161 cases per 10,000 after the MMR vaccine was withdrawn. A new study published by McGill University researchers in the July 2006 issue of the journal Pediatrics found that autism rates rose from 52 per 10,000 to 70 per 10,000 in Quebec after the preservative thimerosal was removed from vaccines in 1996.
Many researchers believe that the increase in autism is largely the result of physicians applying broader diagnostic criteria for the condition in recent years. On the other hand, some researchers believe that the incidence of autism spectrum disorders has dramatically increased. In any case, the best medical advice is that whatever the cause of autism turns out to be, parents should not let their fears prevent them from immunizing their children against the very real threats posed by infectious diseases.