retrospective cohort study looked at records of all children born in
Denmark from 1991 to 1998 (537,303 kids), of whom 82% received the MMR
- Those children who were diagnosed with autism by ICD-10 criteria
(316 with autism, 422 with autistic spectrum) were reported to a central
government registry, which was used in this study. Some of these charts
were randomly reviewed in a blinded manner by a child psychiatrist as
part of the study in order to ensure validity.
- Outcomes were presence or absence of diagnosis of autism or autistic
- The following subjects were excluded: 45 kids who had a congenital
disorder that has autistic behavior as a component of their disorder,
and 5028 who either died or emigrated.
- Method of analysis: Data was broken down into person-years, with
children assigned to non-vaccinated group until the time that they were
vaccinated, if it occurred. Analysis also looked at temporal relationship
of vaccine administration to see if a dose-effect response was seen.
Logistic regression analysis was used.
- Results: for autistic disorder, RR 0.92 with 95% CI 0.68 to 1.24.
For autistic spectrum disorders, RR 0.83 with 95% CI 0.65 to 1.07. These
findings support the null hypothesis (no association between autism
and MMR vaccine).
- Applicability: Vaccine strains identical to those used in USA, age
of administration similar to USA, and diagnostic criteria similar to
those used in the USA.
- Validity and limitations: There may exist subgroups with predispositions
that have not yet been identified. However, given the results and the
large size of this study, such groups would have to either be small
in size or the predisposition be minor in effect. Even if we feel that
this study was good, we still cannot exclude that MMR vaccine may cause
or contribute to autism in some children. However, we can say that if
such an effect is present, it must be small. Such an effect could be
outweighed by risk of diseases prevented by the vaccine.