KM, A Hviid, M Vestergaard, D Schendel, J Wohlfahrt, P Thorsen,
J Olsen and M Melbye 2002. A population-based study of measles,
mumps and rubella vaccination and autism. New
England Journal of Medicine 347:1477-82.
the largest study yet conducted examining possible links between
autism and the vaccination for measles, mumps and rubella (MMR),
Madsen et al. find no hint of an association.
A theory linking MMR with autism had grown out of observations that
children without hints of autism early in their childhood then developed
autism after vaccination.
paper does not address the question of whether or not vaccines
containing a mercury-based preservative, thimerosal, may cause autism,
as the MMR vaccine as formulated by Merck does not contain thimerosal
list of vaccines containing thimerosal). According to the authors
of this study, the form of the MMR vaccine used in Denmark is identical
to that used in the US. Mercury is a powerful neurotoxicant which
alters patterns of brain development. Whether or not it causes autism
is the focus of a huge debate.
an in-depth review of the strengths and weaknesses of this study,
see comments at Safe
did they do? Madsen et al. examined the health
records of all children born in Denmark from 1991 through 1998:
537,303 children of whom 440,655 (82.0 percent) had received the
MMR vaccine and 96,648 had not. Records also allowed them to identify
children diagnosed with autism and related disorders. Of those diagnosed,
they carried out detailed assessments of the records of 13%, and
found it necessary to reclassify only 8% of the 13% (or roughly
1% of the total). The diagnosis used in this detailed assessment
was consistent with that employed by the US CDC in its survey of
Brick Township, New Jersey.
The MMR vaccine was first used in Denmark in 1987. The Danish version
is identical to that used in the United States.
did they find? Among the children in the study, 316 children
were diagnosised with autism and 422 with other autistic-spectrum
the key comparison, Madsen et al. found no elevation of
risk of autism in vaccinated children vs. unvaccinated. Adjusting
for potential confounding variables, the relative risk for vaccinated
children was 0.92 (with 95% confidence intervals extending from
0.68 to 1.24). They found a similar result for other autistic-spectrum
disorders (RR = 0.83; 95% CI from 0.65 - 1.07).
RR of 1 would have indicated exactly equivalent risk. An RR less
than 1 suggests that there is less likelihood of autism in vaccinated
kids, but it only becomes interesting when the range of risk values
bracketed by the 95% confidence intervals no longer include 1. As
long as the range of RR values bracketed by the lower and higher
95% CI includes 1, then the difference between the calculated RR
and 1 is likely to be due to chance.]
Danish data also allowed Madsen et al. to look at the timing
of autism's appearance in relation to when a child was vaccinated.
They found no particular pattern, other than the fact that the average
age at which autism was diagnosed (4 years, 3 months) was later
than the average age at which vaccination occurred (17 months).
does it mean? Madsen et al.'s findings offer strong
evidence against the role of MMR vaccinations in the causation of
critiques of the study, however, suggest alternative explanations.
Unfortunately, US public health records do not allow comparable
research in the US, where use of thimerosal in vaccines is widespread.