The alleged link between the measles, mumps, and rubella (MMR) vaccine and autism made by Wakefield et al.¹ engendered significant fear and mistrust of potential side effects of vaccination, leading to increased immunization refusal. Though the original article was retracted due to the use of fraudulent data, the rising incidence of autism and related diagnoses has fueled persistent interest in the suggested correlation. Earlier studies looking at the relationship were either case series or cross sectional; this was the first study assessing the association between MMR vaccine and autism that was adequately powered.

To assess the RR of MMR vaccination and diagnosis of autism or autism spectrum disorder (ASD).

Retrospective cohort study reviewing 6 national registries of all children born in Denmark from 1991 to 1998.