Immunization and children at risk for autism.

Possible connections between immunization and developmental disorders, most notably autistic disorders, have been the subject of a great deal of debate and have caused much concern for parents who want to make the safest choices for their children. Anxiety has risen steadily since the mid-1990s, when a medical investigative team led by A Wakefield postulated that the measles-mumps-rubella (MMR) vaccine may be a causative factor in the development of autism spectrum disorder. Since this initial publication, immunization remains controversial for some parents and the uptake of the MMR vaccine has fallen in some countries, despite much discussion regarding the safety of MMR, a lack of evidence for an association between MMR and autism, and the risks of insufficient protection against wild measles virus infection. The Canadian uptake of MMR in 1998 was 95%, but data do not exist to document any change in Canada since that time. Many clinicians are concerned that the uptake in younger siblings of children with autism is considerably lower.Further anxiety for parents has been caused by the suggested association between developmental disorders and mercury toxicity due to thimerosal, which is used as a preservative in some vaccines. Many Canadian parents, while continuing to seek chelation therapy in response to this suggestion, are not aware that, in Canada, thimerosal has never been added to MMR, and has not been present in diphtheria-pertussis-tetanus-poliomyelitis or pentavalent vaccines since 1992. It is found in only Hepatitis B vaccine in some provinces.The present article is intended to be a guide for physicians as they counsel parents.