There has been ongoing controversy surrounding certain vaccines and their relationship to autism. Some parents have been concerned that vaccines, specifically the measles-mumps-rubella (MMR) vaccine and preservatives used in other childhood vaccines, play a role in children developing autism. Some stopped vaccinating their children altogether because of this concern.

Thimerosal in vaccines

Parents questioned whether mercury-containing thimerosal (used as a preservative in vaccines) might cause autism. Today, with the exception of some influenza vaccines, none of the vaccines used in the United States to protect preschool-aged children against 12 infectious diseases contain thimerosal as a preservative. (Influenza vaccine is currently available both with thimerosal as a preservative and preservative-free.) More importantly, studies have not found a link between thimerosal-containing vaccines and autism.^{1, 2}

Vaccine combinations

Parents also questioned whether the MMR vaccine—which combines 3 vaccines into 1 injection—causes autism since symptoms of the disorder often become apparent about the time children start getting immunized.

In response to this concern, researchers in Europe, Canada, and the United States looked closely at this issue. Studies have looked at the timing of the vaccine and the vaccine itself and have found no link between the vaccines and autism.

Because the exact cause of this sometimes devastating condition is not known, some parents will continue to have concerns despite the evidence. In these cases, parents should be aware of the risks of serious disease in children who are not vaccinated. In some areas, outbreaks of these dangerous diseases have occurred in people who have not been immunized.