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.