Some parents remain concerned about a possible association between measles-mumps-rubella (MMR) vaccine and autism or autism spectrum disorders (ASDs) in spite of more than 20 published epidemiologic studies showing no link between the vaccines and the disorder. A recently published study adds important information to the available scientific data demonstrating no association between autism/ASD and MMR vaccine.

The original suggestion of an association between measles vaccine and autism or ASD was based in part on studies that showed the presence of measles virus RNA in intestinal tissue taken from children with autism spectrum disorders who also had gastrointestinal (GI) tract symptoms. This report led to the hypothesis that in some children, persistent replication of measles virus in the intestinal tract could lead to inflammatory changes, which would allow neuroactive chemicals to enter the circulation and ultimately result in autistic neurodevelopmental changes.

The recent case-control study, comparing children with autism or ASD and GI symptoms to an age-matched control group of children with GI symptoms without autism or ASD, was published on-line in the Public Library of Science on Sept 4. (http://dx.plos.org/10.1371/journal.pone.0003140). This study  provides definitive evidence to reject

The United States is experiencing a record number of measles cases, but immunizing children on time can help prevent the disease from spreading.

the hypothesis that measles vaccine or MMR vaccine is associated with autism/ASD and GI disturbances.

The study, by Hornig M, et al, was performed at the Center for Infection and Immunity at the Mailman School of Public Health at Columbia University, the Centers for Disease Control and Prevention, Massachusetts General Hospital Adan Trinity College Dublin.

Ileal and cecal biopsy specimens from 25 children with autism/ASD and GI symptoms and 13 age-matched children with only GI disturbances who were undergoing ileocolonoscopy for clinical indications were examined. To be eligible for the study, a child needed to have received at least one dose of MMR vaccine. All children in the study completed a diagnostic evaluation that confirmed the diagnosis of autism or ASD in the patient group and documented normal development in the control group.

The two groups were well matched. The first dose of MMR vaccine was given at a median age of 15.3 months in the children with autism/ASD and 16 months in the control group. There was no difference in the number of cases and controls who had received a second dose of MMR vaccine (20% vs. 31%). The median age at the time of intestinal biopsy was 5.5 years and 5.1 years, respectively. The GI abnormalities were similar in the two groups. Three laboratories, blinded to the diagnosis, evaluated bowel biopsy tissue for the presence of measles virus RNA by a real-time reverse transcription polymerase chain reaction (RT-PCR) assay.

All three laboratories reported the same results. Measles virus RNA was found in only two biopsy samples, one form each group of subjects (autism/GI symptoms group, 4%; control group, 8%).

The temporal order of the onset of autism/ASD and GI symptoms relative to the receipt of MMR vaccine and to each other also was examined. no relationship was found between the onset of GI symptoms and administration of MMR vaccine; a similar proportion of cases and controls experienced the onset of GI symptoms after receiving MMR vaccine. For children who developed GI symptoms after receiving MMR vaccine, there was no difference in the interval between vaccination and onset of GI symptoms in the two groups. Few patients received MMR before the onset of GI symptoms and few patients had the onset of GI symptoms before the onset of autism/ASD.

The study demonstrated no significant differences between cases and controls in the low prevalence of detectable measles virus RNA in intestinal tissues and no evidence of a temporal association between administration of MMR vaccine and development of GI symptoms and/or autism/ASD. The authors concluded that their study provides strong evidence against an association between MMR vaccine and autism/ASD or the GI disturbances seen in some patients with autism/ASD.

This data should further reassure parents about the safety of MMR vaccine. This study comes at a critical time when the United States has had the highest number of measles cases reported in the first six months of the year since 1996. Most of the measles cases in 2008 have occurred in people who are unvaccinated or whose vaccine status is unknown. In the outbreaks reported this year, unvaccinated infants and children have contracted measles while traveling overseas to areas where measles virus is circulating and within the United States after exposure to these imported cases. More than 20% of patients have been hospitalized.

Measles is a serious disease with a number of significant complications and mortality rate of one in 1,000 cases. Children should be immunized on schedule, as they reach the age for which the vaccine is recommended, to reduce the risk of acquiring measles.