Am I alone in feeling somewhat unsatisfied by the official rebuttal of possible
risks associated with the combined Measles-Mumps-Rubella vaccination, in the
news today?
The article that started it is by A J Wakefield et al. The Lancet vol 351 (9103)
1998, 637-641, and it may be located by searching on http://www.thelancet.com/
Its appearance led to a Committee being set up by the Chief Medical Officer of
Health whose conclusions were made public today.
The pathologies of interest are behavioural/neurological (autism; psychosis;
possible encephalitis; -> developmental regression) and intestinal, reported
for 12 children. The authors point out "association in time with possible
environmental triggers" and in discussion say "We have identified a chronic
enterocolitis in children that may be related to neuropsychiatric dysfunction.
In most cases, onset of symptoms was after measles, mumps, and rubella
immunisation. Further investigations are needed to examine this syndrome and
its possible relation to this vaccine."
They also say: "We did not prove an association between measles, mumps, and
rubella vaccine and the syndrome described. Virological studies are underway
that may help to resolve this issue."
Regarding the asociation in time, the picture from their data is less clear
concerning the intestinal pathology than for the behavioural disorder, for
which the following table may be derived from their data (ages in months):
Age at MMR: 12 13 14 15 15 15 16 16 19 21
Age at onset: 12.25 13.5 14.1 15.25 15.25 16 18 18 19.25 21.05
leaving out 1 child for which onset followed 3 months after simple measles
vaccination at 15 months but dramatic behavioural deterioration immediately
followed MMR at 4.5 years; and 1 child with onset at 15 months with "previous
MMR" for which the "apparent precipitating event" was an attack of measles.
In the "Commentary" in the same issue of "The Lancet", by Robert T Chen and
Frank DeStefano, the time-association is addressed as follows: "A first dose of
MMR vaccine is given to about 600 000 children every year in the UK, most
during the second year of life, the time when autism first becomes manifest.
Not surprisingly, therefore, some cases will follow MMR vaccination."
Essentially the same reasoning was used in the 37-person Chief Medical Officer's
Committee rebuttal today.
Chen and DeStefano also say "Biased case-ascertainment, as in this study, will
exaggerate the association", which may be fair enough.
COMMENT: It is clear from the above table that, for these cases, given the
spread of Age at MMR there is an EXTREMELY strong statistical association with
Age at onset (even had cases been selected for onset following after MMR). This
nullifies the rebuttal "Not surprisingly ... " above.
The other major points from the Committee's statement are
1. "There is no evidence to indicate any link between MMR vacccination andbowel
disease or autism"
2. "There is a need for more research generally into the causes of Crohn's
disease, ulcerative colitis and autism".
COMMENT: It will be clear from a reading both of the Lancet paper and of the
Commentary, referred to above, that for this investigation there is plenty of
room for selection/ascertainment/recall/other bias, and for a good number of
covariates to play an explanatory role. This does not diminish the conclusion
that, statistically, it is clear that *something* is going on; but then the
question is: *What* is going on?
The official rebuttal, however, tends to suggest that *nothing* is going on,
and certainly fails to adduce any evidence that whatever it is that clearly *is*
going on is any particular alternative to the possibility that MMR vaccination
may precipitate the events reported. It does NOT acknowledge the strong
statistical association noted above.
Do I detect a vagueness reminiscent of the early days of BSE discussion?
Comments welcome. I have copied this to
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should you feel that further discussion might be more appropriate elsewhere.
Best wishes to all,
Ted.
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E-Mail: (Ted Harding) <[log in to unmask]>
Date: 25-Mar-98 Time: 01:00:58
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