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Time trends in autism and in MMR immunization coverage in California
L Dales1, S J Hammer, N J Smith
1Immunization Branch, California Department of Health Services, 2151 Berkeley Way, Room 712, Berkeley, CA 94704, USA. ldales@dhs.ca.gov
Context:
Considerable concern has been generated in the lay and medical communities by a theory that increased measles-mumps-rubella (MMR) immunization among young children may be the cause of an apparent marked increase in autism occurrence.
Objective:
To determine if a correlation exists in secular trends of MMR immunization coverage among young children and autism occurrence.
Design, Setting, And Participants:
Retrospective analyses of MMR immunization coverage rates among children born in 1980-1994 who were enrolled in California kindergartens (survey samples of 600-1900 children each year) and whose school immunization records were reviewed to retrospectively determine the age at which they first received MMR immunization; and of autism caseloads among children born in these years who were diagnosed with autism and were enrolled in the California Department of Developmental Services regional service center system.
Main Outcome Measures:
Measles-mumps-rubella immunization coverage rates as of ages 17 months and 24 months and numbers of Department of Developmental Services system enrollees diagnosed with autism, grouped by year of birth.
Results:
Essentially no correlation was observed between the secular trend of early childhood MMR immunization rates in California and the secular trend in numbers of children with autism enrolled in California's regional service center system. For the 1980-1994 birth cohorts, a marked, sustained increase in autism case numbers was noted, from 44 cases per 100 000 live births in the 1980 cohort to 208 cases per 100 000 live births in the 1994 cohort (a 373% relative increase), but changes in early childhood MMR immunization coverage over the same time period were much smaller and of shorter duration. Immunization coverage by the age of 24 months increased from 72% to 82%, a relative increase of only 14%, over the same time period.
Conclusions:
These data do not suggest an association between MMR immunization among young children and an increase in autism occurrence.
Insights
This study found no link between measles-mumps-rubella (MMR) vaccination rates and autism diagnoses in California children. Despite rising autism cases, MMR immunization coverage showed minimal change, refuting a causal relationship.
Area of Science:
- Pediatric Health
- Immunology
- Developmental Neuroscience
Background:
- Public concern exists regarding a potential link between measles-mumps-rubella (MMR) vaccination and increased autism rates in children.
- This theory has prompted significant discussion within both medical and lay communities.
Purpose of the Study:
- To investigate the potential correlation between trends in MMR immunization coverage in young children and the occurrence of autism.
- Analyzing secular trends to determine if changes in vaccination rates parallel changes in autism diagnoses.
Main Methods:
- Retrospective analysis of MMR immunization records for children born between 1980-1994 in California kindergartens.
- Review of autism caseload data from the California Department of Developmental Services for the same birth cohorts.
- Correlation analysis between MMR immunization coverage at 17 and 24 months and autism diagnoses by birth year.
Main Results:
- No significant correlation was observed between early childhood MMR immunization rates and autism occurrence trends in California.
- Autism case numbers significantly increased (373% relative increase) from 1980 to 1994.
- MMR immunization coverage by 24 months showed a modest increase (14% relative increase) during the same period.
Conclusions:
- The study's findings do not support an association between MMR immunization in young children and an increased incidence of autism.
- Data suggest that the rise in autism diagnoses is not attributable to MMR vaccination rates.
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