Vaccines and Autism
While researchers agree autism is probably rooted in genetic factors, nobody has determined exactly which genes (or how many) may be involved, and studies of identical twins prove that autism is not a solely genetic disorder. Researchers continue to look for other factors that may 'trigger' an existing genetic predisposition to autism.
One factor many people suspect plays a role in some cases of autism is combined childhood vaccinations. The combined MMR (measles, mumps, rubella) vaccine is the most common suspect. Many parents of autistic children report that otherwise normal infants first showed autistic symptoms shortly after receiving this vaccine. Other families report onset of symptoms after their child received a combined DPT (diptheria, pertussis, tetanus) vaccine.
Many parents have pushed for greater availability of individual vaccines in place of the combined shots, as there seems to be no risk if each vaccine is administered separately. Various factors are suspected as to why combined vaccines may be dangerous. Some suggest receiving three immunizations at once may overload the child's already sensitive immune system. Others point to the presence of mercury as a preservative in the vaccines as a toxin triggering the onset of autistic symptoms. Either of these theories may play a role in the onset of regressive autism, but neither is a certainty.
However the options for testing these ideas are virtually nonexistent. Researchers do not know for certain which genetic markers in a seemingly normal infant may indicate susceptibility for vaccine-triggered autistic symptoms. Getting 'special' versions of the vaccines (only two of three immunizations, with and without mercury, etc.) would be difficult. And even if those problems were eliminated, scientists would have to rely on the genetic markers that could be duplicated in mice (which might eliminate one or more needed for creating autism), because testing on humans would be ethically impossible.
In the meantime, statistical studies seem to show elevated risk, but unfortunately do not reveal which children may be affected. In the meantime, concerned parents can insist on separate vaccinations for their children, where they're available, and join lobbying efforts to make individual vaccines available under insurance systems that may not currently cover them.