Does the MMR vaccine cause autism?
No. The U.S. Institute of Medicine (IOM) has conducted evidence-based reviews and has rejected any causal associations between the measles-mumps-rubella (MMR) vaccine and autism spectrum disorders in children. In addition, a large Danish study of all children born in Denmark between 1991 and 1998 (537,303 children) concluded there was no difference in the rates of autism between vaccinated and unvaccinated children. A Montreal study of 27,749 children born from 1987 to 1998 also concluded there was no relationship between pervasive developmental disorder (autism) rates and a 1-or 2-dose measles-mumps-rubella immunization schedule.
Some speculation has tried to link thimerosal in the MMR vaccine to autism, but the MMR vaccine routinely used in Canada has never contained thimerosal. DTaP, polio and Hib vaccines have not contained this preservative since 1997-98.
Although the reason for the increase in autism is not yet conclusively known, one explanation may be the broader definition and inclusion of many more behaviours and learning disorders within autistic spectrum disorders.
Public Health Agency of Canada. Canadian Immunization Guide. Evergreen edition. http://www.phac-aspc.gc.ca/publicat/cig-gci/index-eng.php (external link)
Canadian Paediatric Society. Your Child’s Best Shot, 4th edition (external link)
U.S. Centers for Disease Control and Prevention. Autism Spectrum Disorders (external link)