CDC Director Dr. Julie Gerberding has delivered a potentially explosive
re****t to the powerful House Appropriations Committee, in which she admits
to a startling string of errors in the design and methods used in the
CDC's
landmark 2003 study that found no link between mercury in vaccines and
autism, ADHD, speech delay or tics.
Gerberding was responding to a 2006 re****t from the National Institute of
Environmental Health Sciences (NIEHS), which concluded that the CDC's
flag****p thimerosal safety study was riddled with "several areas of
weaknesses" that combined to "reduce the usefulness" of the study.
"CDC concurs," Dr. Gerberding wrote in an undated mea culpa to Congress,
(provided to me through a Capitol Hill staffer) adding that her agency
"does
not plan to use" the database in question, the Vaccine Safety Datalink,
(VSD) for any future "ecological studies" of autism.
In fact, Gerberding's re****t said, any continued use of the VSD for
similar
ecological studies of vaccines and autism "would be uninformative and
potentially misleading."
Ecological vaccine studies are large, epidemiological analyses of risks
and
trends using computerized data from large populations -- in this case
children enrolled at several big HMOs -- without ever examining a single
patient in person.
CDC officials conducted at least five separate analyses of the data over a
four-year period from 1999-2003. The first analysis showed that children
exposed to the most thimerosal by one month of age had extremely high
relative risks for a number of outcomes, compared with children who got
little or no mercury: The relative risk for ADHD was 8.29 times higher,
for
autism, it was 7.62 times higher, ADD, 6.38 times higher, tics, 5.65
times,
and speech and language delays were 2.09 more likely among kids who got
the
most mercury.
Over time, however, all of these risks declined into statistical
insignificance, statistical inconsistency or else outright oblivion: The
relative risk for autism plummeted from 7.62 in the first analysis, to
2.48
in the second version, to 1.69 in the third round, to 1.52 in the fourth,
and down to nothing at all in the fifth, final, and published analysis
printed in the Journal Pediatrics in November of 2003.
Vaccine officials attributed the steady drop to the elimination of
"statistical noise" from the data through due diligence and the endeavor
for
excellence in governmental statistical analysis.
Indeed, the VSD study was the main pillar of a hugely influential 2004
re****t by the Institute of Medicine, which also concluded that there was
no
evidence of link between mercury, vaccines and autism.
To this day, public health officials routinely point to five "large
epidemiological studies" representing the "highest quality science," none
of
which found any link to thimerosal.
In fact, the American VSD study has long been held up as the best and
brightest of them all (the others were in Sweden, the UK, and two in
Denmark). And this reputation has stuck in the minds of medicine and the
media.
Curiously though, even the study's lead author -- Dr. Thomas Verstraeten,
an
employee of vaccine maker GlaxoSmithKline -- protested that the VSD study
"found no evidence against an association, as a negative study would. In
fact, he said that additional study was needed, which "is the conclusion
to
which a neutral study must come."
That's when Congress stepped in.
In 2005, a group of Senators and Representatives headed by Sen. Joe
Lieberman wrote to the NIEHS (an agency of the National Institutes of
Health) saying that many parents no longer trusted the CDC to conduct
independent minded studies of its own vaccine program. Lieberman et al
asked
NIEHS to review the CDC's work on the vaccine database and re****t back
with
critiques and suggestions.
The final NIEHS re****t was a serious and thoughtful critique of where the
CDC went wrong in its design, conduct and analysis of the study. The NIEHS
panel "identified several serious problems," with the CDC's effort,
criticism to which the agency had not responded -- until now.
In her letter to the House Appropriations Committee, the CDC Director
responded directly to many -- though not all -- of the most im****tant
criticisms and recommendations contained in the NIEHS panel re****t.
For example, the NIEHS had criticized CDC for failing to account for other
mercury exposures, including maternal sources from flu shots and immune
globulin, as well as mercury in food and the environment.
"CDC acknowledges this concern and recognizes this limitation," the
Gerberding reply says.
The NIEHS also took CDC to task for eliminating 25% of the study
population
for a variety of reasons, even though this represented, "a susceptible
population whose removal from the analysis might unintentionally reduce
the
ability to detect an effect of thimerosal." This strict entry criteria
likely led to an "under-ascertainment" of autism cases, the NIEHS
re****ted.
"CDC concurs," Gerberding wrote, again noting that its study design was
"not
appropriate for studying this vaccine safety topic. The data are intended
for administrative purposes and may not be predictive of the outcomes
studied."
Another serious problem was that the HMOs changed the way they tracked and
recorded autism diagnoses over time, including during the period when
vaccine mercury levels were in decline. Such changes could "affect the
observed rate of autism and could confound or distort trends in autism
rates," the NIEHS warned.
"CDC concurs," Dr. Gerberding wrote again, "that conducting an ecologic
analysis using VSD administrative data to address potential associations
between thimerosal exposure and risk of ASD is not useful."
Read that sentence one more time. The head of the CDC is saying that its
most powerful and convincing piece of exonerating evidence for thimerosal
is, in effect, "useless."
I hope everyone will read it, including the recommendations to make the
VSD
better, and the CDC's agreement with all of the suggestions.
As questionable at the US thimerosal study was, "it was an improvement on
other studies, including the two in Denmark, both of which had serious
weaknesses in their designs," Dr. Irva Hertz-Picciotto, Professor of
Public
Health at UC Davis Medical School and Chair of the NIEHS panel, told
re****ter Dan Olmsted at UPI.
That leaves very little for the CDC to go on in terms of proving that
thimerosal and autism are not associated in any way.
Yes, there is always the study of disability services data from
California -- which seem to be rising among the youngest cohorts of kids,
who presumably received little or no mercury because thimerosal was
largely
removed from childhood shots.
But California is an "ecological study" with problems of its own.
"Although (this) information is often used by media and research entities
to
develop statistics and draw conclusions, some of these findings may
misrepresent the quarterly figures," cautions the website of the
California
Department of Developmental Services (DDS). "Increases in the number of
persons re****ted from one quarter to the next do not necessarily represent
persons who are new to the DDS system."
Even the CDC admits that "there are several limitations" with linking a
VSD
study design with the California data, Gerberding wrote to Congress,
because, among other things, California only counts "persons who were
referred to and/or voluntarily entered" the disability system."
It will be interesting to see how the House Committee -- and the
mainstream
media -- react to this rather breathtaking confession by the CDC, which
does
seem to want to conduct the best vaccine-autism science possible (see
Gerberding's replies to NIEHS recommendations for improving the VSD: CDC
officials are currently conducting in- depth follow up studies with VSD
patients).
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