New Canadian Study Rules Out PDD (Autism) Link to Thimerosal and/orMMR Vaccines

Pervasive Developmental Disorders in Montreal, Quebec, Canada:
Prevalence and Links With Immunizations
Eric Fombonne, MDa, Rita Zakarian, MEda, Andrew Bennett, PhD, CPsychb,
Linyan Meng, MSca and Diane McLean-Heywood, MAb

a Department of Psychiatry, McGill University, Montreal Children's
Hospital, Montreal, Quebec, Canada
b Lester B. Pearson School Board, Montreal, Quebec, Canada

BACKGROUND. The prevalence of pervasive developmental disorders has
increased in recent years. Links with the measles component of the
measles-mumps-rubella vaccine and the cumulative exposure to thimerosal
through other vaccines have been postulated.

OBJECTIVES. The purpose of this work was to estimate the pervasive
developmental disorder prevalence in Montreal, Canada, in cohorts born
from 1987 to 1998 and evaluate the relationship of trends in pervasive
developmental disorder rates with: (1) changes in cumulative exposure to
ethylmercury (thimerosal) occurring through modifications in the
immunization schedule of young children and (2) trends in
measles-mumps-rubella vaccination use rates and the introduction of a
2–measles-mumps-rubella dosing schedule during the study period.

METHODS. We surveyed 27749 children born from 1987 to 1998 attending 55
schools from the largest Anglophone school board. Children with
pervasive developmental disorders were identified by a special needs
team. The cumulative exposure by age 2 years to thimerosal was
calculated for 1987–1998 birth cohorts. Ethylmercury exposure ranged
from medium (100–125 µg) from 1987 to 1991 to high (200–225 µg) from
1992 to 1995 to nil from 1996 onwards when thimerosal was entirely
discontinued. Measles-mumps-rubella coverage for each birth cohort was
estimated through surveys of vaccination rates. The immunization
schedule included a measles-mumps-rubella single dose at 12 months of
age up to 1995, and a second measles-mumps-rubella dose at 18 months of
age was added on after 1996.

RESULTS. We found 180 children (82.8% males) with a pervasive
developmental disorder diagnosis who attended the surveyed schools,
yielding a prevalence for pervasive developmental disorder of 64.9 per
10000. The prevalence for specific pervasive developmental disorder
subtypes were, for autistic disorder: 21.6 of 10000; for pervasive
developmental disorder not otherwise specified: 32.8 of 10000; and for
Asperger syndrome: 10.1 of 10000. A statistically significant linear
increase in pervasive developmental disorder prevalence was noted during
the study period. The prevalence of pervasive developmental disorder in
thimerosal-free birth cohorts was significantly higher than that in
thimerosal-exposed cohorts (82.7 of 10000 vs 59.5 of 10000). Using
logistic regression models of the prevalence data, we found no
significant effect of thimerosal exposure used either as a continuous or
a categorical variable. Thus, thimerosal exposure was unrelated to the
increasing trend in pervasive developmental disorder prevalence. These
results were robust when additional analyses were performed to address
possible limitations because of the ecological nature of the data and to
evaluate potential effects of misclassification on exposure or
diagnosis. Measles-mumps-rubella vaccination coverage averaged 93%
during the study interval with a statistically significant decreasing
trend from 96.1% in the older birth cohorts (1988–89) to 92.4% in
younger birth cohorts (1996–1998). Thus, pervasive developmental
disorder rates significantly increased when measles-mumps-rubella
vaccination uptake rates significantly decreased. In addition, pervasive
developmental disorder prevalence increased at the same rate before and
after the introduction in 1996 of the second measles-mumps-rubella dose,
suggesting no increased risk of pervasive developmental disorder
associated with a 2–measles-mumps-rubella dosing schedule before age 2
years. Results held true when additional analyses were performed to test
for the potential effects of misclassification on exposure or diagnostic
status. Thus, no relationship was found between pervasive developmental
disorder rates and 1- or 2-dose measles-mumps-rubella immunization
schedule.

CONCLUSIONS. The prevalence of pervasive developmental disorder in
Montreal was high, increasing in recent birth cohorts as found in most
countries. Factors accounting for the increase include a broadening of
diagnostic concepts and criteria, increased awareness and, therefore,
better identification of children with pervasive developmental disorders
in communities and epidemiologic surveys, and improved access to
services. The findings ruled out an association between pervasive
developmental disorder and either high levels of ethylmercury exposure
comparable with those experienced in the United States in the 1990s or
1- or 2-dose measles-mumps-rubella vaccinations.

http://pediatrics.aappublications.or...act/118/1/e139
© 2006 American Academy of Pediatrics. All rights reserved.

also:

http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_docsum



---------------------

Of course, the anti-vac liar crowd has already jumped all over this
study, as it destroys several of their pet lies.

For further information on the trashing of the authors of this study,
and a demonstration of how SafeMinds, et al, lie:

http://www.kevinleitch.co.uk/wp/index.php?p=392

---------------------

My comment:

When taken with all of the other population based studies, it is clear
that there is no evidence supporting a MMR/thimerosal-autism link.

It is time to move on, and spend precious research money elsewhere.