http://www.jr2.ox.ac.uk/bandolier/band86/b86-4.html
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Bandolier |
Bandolier Library |
More on MMR and autism
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If you came to a small
Oxfordshire village during the day and counted the number of lights that were
on, you would find few. Come at night and you would find many. One conclusion
might be that putting the lights on has caused it to become dark. Part of the
MMR-autism debate (Bandolier 84)
has involved a similar observation, that autism was rare and now is common,
and MMR was rare and now is common. Presto, MMR causes autism! It may be a bit more
complicated than that. Two new studies [1,2] have examined the temporal
relationship between MMR vaccination rates and autism. Autism is on the
increase despite high and stable MMR vaccination rates. UK study
One study from Boston is based on the UK General Practice Research
Database. It identified 305 children (254 boys) aged 12 or younger whose
diagnosis of autism was first recorded between 1988 and 1999. The peak age of
first diagnosis was at years 3 and 4, but with a substantial number being
diagnosed at six years or older. The number of cases and incidence of autism
increased substantially and constantly over the period (Figure). Figure: Total number of cases of autism and incidence per 10,000 person
years in UK
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The study included a
detailed analysis of 114 boys born in 1988-1993 who had a first recorded
diagnosis of autism at ages 2-5 years. For them the four-year risk of
diagnosed autism rose from 8 per 10,000 for boys born in 1988 to 29 per
10,000 for boys born in 1993 while the MMR vaccination rate was constant at
about 97%. California study
The California study
used data from 21 Regional centres covering all of California, and for the
years 1980 to 1994. MMR immunisation rates by two years of age were about 72%
before 1988 and about 82% afterwards, with the same preparation used since
1979. During this time the number of cases of autism, about 200 in 1980,
increased inexorably to about 1200 by 1994. The trend for increasing autism
in California persisted long after the introduction of MMR vaccination, and
was not affected by a modest increase in immunisation rates in the mid 1980s.
Comment
This continuous upward
trend in autism dating from the late 1970s or early 1980s has been seen
before in a study from North Thames [3]. We now have three studies, all
showing this inexorable rise irrespective of whether immunisation rates are
high and uniform, or pretty high and getting higher. MMR has been available
and been used for years. None of these studies supports, and all refute, that
autism is caused by MMR vaccination, or that MMR vaccination is responsible
for a major number of cases of autism. What these studies all
confirm is that autism, especially among boys, is on the increase. We don't
know why. There is a plan for a further large case-control study using the
UKGPRD [4]. It is predominantly to examine the link between MMR and autism,
but may provide clues about links with environmental or other factors linked
with autism. References:
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