Autism and MMR Immunisation Trends in California Birth Cohorts, 1980–1994
- Vaccine Affect
- Jul 7
- 2 min read
Updated: Sep 15
Time Trends in Autism and in MMR Immunization Coverage in California
Dales L, Hammer SJ, Smith NJ
JAMA. 2001;285(9):1183–1185
doi:10.1001/jama.285.9.1183
This study examined whether the rise in autism diagnoses in California from 1980 to 1994 correlated with increased MMR (measles-mumps-rubella) vaccination among young children. Using state health and education records, researchers compared MMR immunisation rates at 17 and 24 months of age with autism caseloads recorded by the California Department of Developmental Services. While autism diagnoses rose sharply—by 373% from 44 per 100,000 live births in 1980 to 208 per 100,000 in 1994—MMR coverage increased only modestly by 14%, from 72% to 82% by 24 months. The increase in autism cases began years before the slight rise in vaccine uptake and continued steadily even after vaccine coverage plateaued.
The study concludes there is no evidence to support a causal link between MMR vaccination and increased autism occurrence. Researchers emphasise that multiple other factors likely contributed to the rise in autism diagnoses, such as greater public awareness, broader diagnostic criteria, and improved access to developmental services.
Correspondance
In 2001, a study by Dales and colleagues concluded that there was “essentially no correlation” between rates of autism in California and uptake of the measles-mumps-rubella (MMR) vaccine. However, their findings were challenged in a published reply by Edwardes and Baltzan, who argued that the way the graph in the original paper was scaled created an optical illusion that minimised the apparent relationship. When they recalculated using the same data, they reported strong statistical correlations (0.73 for immunisation by 24 months and 0.90 for immunisation by 17 months). This debate highlights how scientific conclusions can sometimes be influenced by the way data are presented and interpreted, and why independent re-analysis and transparency in methodology are important when addressing sensitive public health issues such as vaccines and autism.
