Thimerosal: A Missing Link in Denmark MMR-Autism Study (11/7/02)
Today, the New England Journal of Medicine has published an article which
refutes a link between MMR and autism using epidemiology. This study was
released last week to the major media by the CDC, its major funder along
with NAAR. Since then, the CDC PR machine has been working very hard to spin
the conclusions their own way. Obviously, they want to put an end to any
more discussions and research on vaccines and autism.
However, while the study methodology appears to be good, and there is much
to learn from the informative findings, there are some significant
shortcomings in the conclusions drawn and the study results raise more
questions than they answer and underscore the importance for more research.
For example, one of the most concerning omissions of the study was their
failure to consider the absence of Thimerosal in the other infant vaccines
the children of the Danish study received prior to getting their MMR
Although she did not include it in her article, the reporter from the Dallas
Morning News who interviewed me (article below) was able to confirm that the
mercury based preservative under so much legal fire for triggering autism
was removed from vaccines on the market in Denmark prior to the birthdates
of the children studied. American children on the other hand, have
potential cumulative mercury exposures at sometimes neurotoxic levels from
prenatal exposures including maternal vaccination and immune globulin
preparations, environmental pollution and infant vaccinations which create a
significantly different set of circumstances when the MMR vaccine, which
does not contain mercury, is administered.
We feel very strongly that it is erroneous for the study's authors to
conclude that since the children in the Danish study did not show an
increased incidence of autism after MMR vaccine that the same would hold
true for all children. They have not satisfied the question of the MMR
vaccine's potential role as a trigger amidst other environmental factors
including previously administered mercury containing vaccines that have been
given to children outside of their population. It is entirely possible, but
not yet studied by the CDC, that a child's immune response, inhibited by the
elevated mercury levels from thimerosal-containing vaccinations, has less
ability to respond to the measles virus in the MMR vaccine. This might be
an explanation for the presence of measles virus cultured from the brains
and guts of 80 percent of autistic children. However, we are grateful for
their epidemiological research and hopeful that it will spur the absent and
yet much needed biological mechanism research here in the United States.
Sallie Bernard from Safe Minds (www.safeminds.org)
has prepared an
exceptional press release and comprehensive point by point assessment of the
positives and the negatives of this study. We support and agree with the
position of Safe Minds on this study.
Additionally, you may want to pick up the November/December issue of
Mothering Magazine (www.mothering.com) - it
has a sizeable section devoted
to investigating Thimerosal and neurodevelomental delays. It includes
articles by some of the other brains behind Safe Minds - Lyn Redwood and Liz
Birt, articles by mercury expert Dr. Boyd Haley and Autism expert Dr. James
Jeffrey Bradstreet , and an interview with Dr. Stephanie Cave.
Parents Requesting Open Vaccine Education (PROVE)
Denmark Study on Autism and MMR Vaccine Shows Need for Biological Research
Courtesy of Sallie Bernard, Safe Minds (www.safeminds.org)
(Cranford, NJ, November 6) The newly released study on autism and the
measles-mumps-rubella vaccine ("A Population Based Study of Measles, Mumps
and Rubella Vaccination and Autism." New England Journal of Medicine, Vol
347, No 19; Nov 7, 2002: 1477-1483, by Kreesten Meldgaard,et al) is a
welcome addition to autism epidemiology. Unfortunately, the study
conclusions appear overreaching, claiming that this analysis is the final
word on autism and vaccines and implying that more research on the topic is
unnecessary. Safe Minds asserts that other vaccines besides MMR may be
involved in autism, and that only biological research, not epidemiology, can
answer the question of whether the MMR vaccine plays a role in autism.
"It is important to note that the study only focused on the MMR vaccine, and
not vaccines also implicated in autism which contain the mercury
preservative thimerosal," explains Sallie Bernard, executive director of
Safe Minds. "The study also failed to investigate whether the MMR vaccine
might be interacting with the thimerosal from other vaccines to increase the
severity of symptoms in children who already have autism. Finally, the study
did not differentiate between regressive autism, which is the type being
linked to MMR vaccine, and the more prevalent early onset autism, which is
the type being linked to thimerosal."
Safe Minds is an advocacy organization which focuses on the role of mercury
in neurodevelopmental disrorders, including autism. It was founded by
parents of autistic children. Thimerosal contains 50% ethylmercury and has
been used in most recommended childhood vaccines, including the
Diphtheria-Tetanus-Pertussis (DTP), Haemophilus influenzae type B (HiB), and
Hepatitis B (Hep B) vaccines.
Research studies have shown that mercury exposure in utero or during early
postnatal life - the time when thimerosal vaccines are being given - can
cause immune system abnormalities which predispose the child to ongoing
viral infections. It is biologically plausible that this immune disruption
may have allowed the live measles virus component in the MMR vaccine to
persist in susceptible autistic children, making the symptoms of the
disorder worse. This connection would not be detected through an
epidemiology study like the Denmark one. Nor does the Denmark study have the
power to detect differences in rates of regressive autism between vaccinated
and unvaccinated children, since the number of regressive cases - estimated
to be 10%-20% of all autism cases - would be too small.
"The overreaching conclusion of the study should not obscure other important
findings from this extensive and well planned analysis from Denmark,"
continued Ms. Bernard. "The authors report an increased prevalence of
autism in that country, and thus it supports other recent studies that are
also showing increases. This rise tells us that an environmental agent is at
work worldwide that is driving this trend. We believe that thimerosal and
environmental mercury - which are worldwide pollutants - are behind the
surge. Also, Denmark has had lower and later exposures to thimerosal in
vaccines, and the report shows that their rate of autism is lower than in
the US, which is also consistent with a thimerosal connection."
Safe Minds is encouraged that the Centers for Disease Control sponsored such
an extensive study on autism, which shows that this terrible disease is
finally getting the attention of public health officials. Safe Minds looks
forward to increased support for autism research, especially at the
Assessment of the Denmark MMR-Autism Study
"A Population Based Study of Measles, Mumps and Rubella Vaccination and
Autism." New England Journal of Medicine, Vol 347, No 19; Nov 7, 2002:
Kreesten Meldgaard, M.D., Andders Hviid, M.Sc., Mogens Vestergaard, M.D.,
Diana Schendel, P.H.D., Jan Wohlfahrt, M.Sc., Poul Thorsen, M.D., JØrn
Olsen, M.D., and Mads Melbye, M.D.
This study is well done, but due to its design, it cannot be considered the
"definitive" study on autism and the MMR vaccine. Rather, biological
research, not epidemiology, is needed to truly answer the question of a link
between the MMR and regressive autism.
POSITIVE ASPECTS ABOUT THIS STUDY
* The CDC and public health authorities are investing dollars
and efforts into autism research. These efforts should be
applauded, and expanded!
* The study reports a steep rise in autism rates from 1980s to
1990s (from <2.0 to >10.0 per 10,000). Increases are also
being reported in other countries, again suggesting
environmental influences at work, as the recent landmark
MIND Institute epidemiology of California study did.
* The results appear to support a thimerosal role in the
increases in autism being reported in the study in Denmark,
and the fact that Danish autism prevalence is less than in the
US and the UK, where the thimerosal vaccines are given in
larger quantities and/or earlier in life. Further clarification is
needed to elucidate this association; specifically, the
prevalence by birth cohort and the Danish vaccine schedule
and formulations for the time period are needed.
* The study authors acknowledge that previous attempts to
refute the MMR-autism hypothesis were too poorly
designed to reach definitive conclusions. (p.1477, 2nd
paragraph on right)
* The study brings attention to a rich database of information
(i.e., Danish registries) on which additional studies of
autism can be based.
CAUTIONS ABOUT THE STUDY'S CONCLUSIONS ON BEING
THE "DEFINITIVE" STATEMENT ON AUSTISM-MMR
* A vaccine-induced autism subset may be present at a
much lower prevalence in Denmark since the prevalence of
autism is lower in Denmark compared with other countries
(see prevalence comparison table at end of document).
This may indicate a co-factor effect (e.g. thimerosal) that
operates to a greater degree elsewhere.
+ The lower prevalence in Denmark is not a function of
variation in diagnosis, since the same
developed by CDC was used in Brick, Atlanta,
+ Means other environmental factors, rates of factors, or
combination of factors may be at work in
Denmark vs US or
+ It is possible that MMR increases the rate of autism
when acting in conjunction with another
such as mercury. If that factor's prevalence
is not controlled
for among the study groups (vaccinated vs
would obscure the role of MMR as a causative
factor in the
+ This is entirely biologically plausible since mercury
the antiviral immune response, and
and infants are more susceptible to
persistent viral infections.
+ Only psychiatric records were accessed, not medical
so there were no data on gastrointestinal
symptoms and no
taking of CSF or GI samples to detect
presence or absence
of measles virus. Cannot tell if measles
impacting a subgroup of children, if any.
may be increasing the severity of autism,
even if it is not
causing an increase in the number of cases.
* There was no attempt to differentiate between regressive and
early-onset forms of autism. Since the regressive form
comprises a minority of cases - 10%-20% - the power to
detect whether there was a difference in regressive autism
prevalence between MMR vaccinated and non-vaccinated is
lacking in this study.
+ The assertion that a relative risk of autism of less
rules out the possibility that there
are important subgroups
* Although overall well designed, there appear to be some
methodological problems with the study, which need further
elucidation from the investigators and raise questions about
its conclusions of being the "definitive" MMR-Autism study.
+ The study covered 8 birth cohorts, but two of these,
born in 1997 and 1998, were only 1 or 2
years old when the
data records were obtained at the end
of 1999. These age
groups are too young in most cases to
be diagnosed with
autism or to be immunized with the MMR.
This might have
been fine if the impact applied equally
to both vaccinated
and unvaccinated groups. However, fully
half (50.6%) of
the unvaccinated group fell into these
two younger birth
cohorts, vs. just a fourth (27.7%) of
the vaccinated group.
Therefore, in these 2 birth cohorts,
true autism rates will
be underestimated (since they have yet
to be diagnosed)
and unvaccinated status is
+ Children who were in fact vaccinated were assigned to
the unvaccinated group if they were
autism efore they received the MMR. The
cases comprise 10% of the unvaccinated
(13 out of 130). This commingling blurs
between vaccinated and unvaccinated. It
is not clear
what effect this would have on the
+ A number of the measures used to arrive at the
conclusion that autism and autism
disorders were not
associated with MMR vaccination are
irrelevant. Age of
vaccination with MMR, time interval
between receipt of
MMR and diagnosis of autism, and year
vaccination do not help elucidate the
relationship between receipt of MMR and
of measles-related symptoms and
The age of diagnosis is arbitrary and
can vary for many
reasons, among them differences in
severity of illness,
access to care, and clinician skill and
these measures cannot be used to refute
of a temporal relationship between MMR
and onset of
symptoms of measles-related illness and
* As the authors point out on page 1481, they had no
information on the presence or absence of a family history
of autism, which could explain the study's negative findings
only if families with a history of autism avoided MMR
vaccination. It should be noted that in 1993, there was a
widely reported news story in Denmark about a parent
with autistic twins who asserted that their autism was
caused by the MMR vaccine. It is entirely possible that
parents with either (a) a family history of autism or (b) an
infant or toddler with emerging symptoms of autism,
would avoid vaccination at a higher rate than other
parents. This would inflate the unvaccinated group with
children of families predisposed to autism.
A chart showing comparative Reported Rate of Autism from Recent US, UK, and
Denmark Studies can be found on the Safe Minds web page at
Danish study: Autism not linked to vaccination
By SHERRY JACOBSON / The Dallas Morning News
A major new study of half a million children in Denmark offers further
evidence that there is no connection between a common childhood vaccination
and the subsequent development of autism.
Researchers looked at the incidence of autistic disorders among 440,655
Danish children who had received the standard vaccine to prevent measles,
mumps and rubella. Then they compared how often the same disorders appeared
in a group of 96,648 children who were not vaccinated.
The eight-year study, published Thursday in The New England Journal of
Medicine, found the same risk of autism in both groups, providing what the
authors called "strong evidence" against the hypothesis that the vaccine
could be causing autism.
A number of smaller studies in recent years have likewise established no
"Few studies can be said to be conclusive, but I think this is as close as
we can get," said Dr. Kreesten Meldgaard Madsen, an epidemiologist at the
Danish Epidemiology Science Center in Arhus, Denmark, and the study's lead
Eight years of records
The study was drawn from the meticulous health records kept of every child
born in Denmark from 1991 through 1998.
Each childhood vaccination was recorded, as well as subsequent diagnosis of
mental disorders such as autism.
However, the study is unlikely to satisfy parent groups that have targeted
the MMR vaccine as a possible source of their children's medical problems.
"This is not going to put the question to rest for parents whose perfectly
normal children regressed after they received this vaccination," said Dawn
Richardson, president of Parents Requesting Open Vaccine Education, an
Austin-based group that includes about 3,500 families concerned about
Such groups point to several smaller studies that have suggested that some
children experience behavioral problems soon after receiving a measles,
mumps and rubella vaccination at age 18 months. Autism experts have
speculated that behavioral difficulties may become apparent at that age but
be merely coincidental to the timing of vaccination shots.
"Maybe the vaccine is not the cause of autism disorders, but it could be the
trigger," Ms. Richardson speculated. "Maybe it's not happening in Denmark,
but we're saying there's something going on here in the U.S. with the
children who are being vaccinated."
Barbara Low Fisher, co-founder and president of another parent group, the
National Vaccine Information Center, said a Danish study might not apply to
"They are a genetically homogeneous people," Ms. Fisher said of the children
in the Danish study. "And we are not."
Relevance in U.S.?
Dr. Greg Poland, a measles vaccine expert at the Mayo Clinic in Rochester,
Minn., agreed that a study in one country might not always relate to people
in another. However, he noted that many Americans are of Scandinavian
While calling the new study "the single best epidemiological population
study done on this issue," Dr. Poland also said that the findings were
unlikely to convince people who have decided that vaccinations were harmful
for their children.
"You can't change emotion or fear-based decisions with scientific data," Dr.
Poland said. "It is exceedingly difficult for people not to assume cause and
effect in situations like this." He heads the Mayo Vaccine Research Group
and is a professor of medicine and infectious diseases at the Mayo Medical
The combination measles, mumps and rubella vaccine has been in use since
1988, leading some critics to link it to the growing incidence of autism in
the United States and elsewhere. Studies have estimated there were two
autism cases per 10,000 children ages 5 to 9 in the 1980s and early 1990s.
By 2000, the incidence had grown to 10 cases per 10,000 children in the same
However, Dr. Madsen and his colleagues noted in the new study that the
autism increase in the United States and Denmark "occurred well after the
introduction" of the MMR vaccine.
"Also, if there were any association between the MMR vaccination and autism,
we would expect to see a rise in the diagnoses of autism in the time after
vaccination," he said. "We did not see that."