Scientists have differing opinions on the potential connection between the growing number of children with autism and certain childhood vaccines. A recent meeting of federal panel examined various studies on this controversial topic. Some studies showed no link between thimerosal, a mercury-based preservative used in childhood vaccines, and the prevalence of autism. However, other studies indicated the possibility that mercury from vaccines may have played a role. There is also disagreement among scientists regarding the theory that the vaccine for measles, mumps, and rubella causes autism. While some scientists argued that there is still a potential link, others disputed this theory.
These theories have emerged because symptoms of autism usually appear around the age of 2, which coincides with the time children receive vaccines. Consequently, some parents have suspected a connection. Public-health officials are concerned about the implications of this debate. They worry that parents who are concerned about autism might choose not to vaccinate their children against potentially life-threatening diseases.
The Institute of Medicine’s Immunization Safety Review Committee, which provides scientific information to Congress, will examine the information presented at the meeting and release a report on the subject within the next three to six months. In 2001, the committee concluded that there was insufficient evidence to confirm or dismiss a link between vaccines and autism, and called for further research. In the meantime, the committee recommended the removal of thimerosal from childhood vaccines, a measure that has been implemented by vaccine manufacturers since 1999.
Several large-scale studies have been conducted since the committee’s last report, casting doubt on the connection between vaccines and autism. One such study in Denmark, which examined the health records of over 500,000 children, found no difference in the rate of autism between those who received the MMR vaccine and those who did not. Similar conclusions have been reached by other population studies. A recent study of 103,000 British children who received vaccines with thimerosal showed no evidence of an increased risk of autism.
However, some scientists argue that despite these studies, research has shown that children with autism have higher levels of mercury in their systems. One toxicologist hypothesized that autism may be related to the inability of a child’s system to effectively eliminate mercury, even if thimerosal itself is not the cause. Another scientist urged caution in dismissing the link between autism and vaccines, as more research is needed.
Over the past 20 years, the number of reported cases of autism has increased from two to five per 10,000 people to potentially affecting as many as one in 500 people. This makes autism more common than childhood cancer or Down syndrome, according to the National Academy of Sciences.
