Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time-trend analysis

Abstract

Objectives To estimate changes in the risk of autism and assess the relation of autism to the mumps, measles, and rubella (MMR) vaccine. Design Time-trend analysis of data from the UK general practice research database. Setting General practices in the United Kingdom. Participants Children aged 12 years or younger diagnosed with autism between 1988 and 1999, with further analysis of boys aged 2 to 5 years born between 1988 and 1993. Main outcome measures Annual and age-specific incidence for first recorded diagnoses of autism (that is, when the diagnosis of autism was first recorded) in the children aged 12 years or younger; annual birth cohort-specific risk of autism diagnosed in the 2- to 5-year-old boys; and coverage (prevalence) of MMR vaccination in the same birth cohorts. Results The incidence of newly diagnosed autism increased 7-fold, from 0.3/10,000 person-years in 1988 to 2.1/10,000 person-years in 1999. The peak incidence was among 3- and 4-year-olds, and 83% (254/305) of cases were in boys. In an annual birth-cohort analysis of 114 boys born between 1988 and 1993, the risk of autism in 2- to 5-year-old boys increased nearly 4-fold over time, from 8/10,000 (95% confidence interval [CI], 4-14/10,000) for boys born in 1988 to 29/10,000 (95% CI, 20-43/10,000) for boys born in 1993. For the same annual birth cohorts, the prevalence of MMR vaccination was more than 95%. Conclusions Because the incidence of autism among 2- to 5-year-olds increased markedly among boys born in each year separately from 1988 to 1993 while MMR vaccine coverage was more than 95% for successive annual birth cohorts, the data provide evidence that no correlation exists between the prevalence of MMR vaccination and the rapid increase in the risk of autism over time. The explanation for the marked increase in risk of the diagnosis of autism in the past decade remains uncertain.