Immunization Safety Review: Vaccines and Autism

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Immunization Safety ReviewVaccines and Autism

• Marie McCormick
• Chair, Immunization Safety Review Committee
• Presentation to NVAC
• June 2004

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Issue Under Review

• Hypothesized association between vaccines and
  autism, specifically
  
• MMR vaccine and autism
• Thimerosal-containing vaccines and autism
• The committee did not focus on other
  neurodevelopmental disorders

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Why the committee focused on this topic

• Requested by the Interagency Vaccine Group to
  reexamine this issue in its eighth and final
  report.
  
• The committee issued two previous reports in 2001
  examining MMR and autism and thimerosal-containing
  vaccines and neurodevelopmental disorders.
  
• Updated statement from the committee was
  warranted because significant new data have
  emerged, and because the topic remains of such
  considerable controversy.

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Scientific Assessment Causality Conclusions

• The evidence favors rejection of a causal
  relation between both MMR vaccine and
  thimerosal-containing vaccines and autism.
  

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Scientific Assessment Causality Conclusions

• Evidence for MMR and autism finding
• 14 large, well-designed epidemiological studies
  consistently showed no association between the
  MMR vaccine and autism.
  
• This finding is consistent with 2001 report on
  MMR and autism
  

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Scientific Assessment Causality Conclusions

• Evidence for thimerosal and autism finding
• 5 large, well-designed epidemiological studies in
  different countries provided significant evidence
  of no association between TCVs and autism.
  
• 2001 IOM report concluded evidence was inadequate
  to accept or reject relationship between TCVs and
  NDDs. Why different now?
  
• Only one unpublished epi study available then.
  Significantly more research available now.
  
• That report focused on broader set of
  neurodevelopmental outcomes. A potential
  biological mechanism exists for those outcomes by
  way of analogy with methyl mercury, but not for
  autism

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Scientific AssessmentBiological Mechanisms

• Potential biological mechanisms put forth as
  possible explanations for how vaccines might
  cause autism
  
• The release of chemicals into the brain due to
  disruption of intestinal function by the MMR
  vaccine
  
• Triggering of abnormalities in the immune system
  that are indicative of vaccine-induced damage to
  the CNS
  
• Increased accumulation of and decreased excretion
  of mercury from the brains of a subgroup of
  children
  
• The effects of thimerosal on a variety of
  biochemical pathways

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Scientific AssessmentBiological Mechanisms

• Evidence comes from in vitro experimental
  systems, clinical observations, and analogies
  between rodent behavior and human behavior.
  
• While the laboratory observations of the toxic
  effects of mercury are important, these
  observations do not explain how specific
  exposures in a rapidly developing infant affect
  certain tissues but not others where these
  mechanisms are also active.
• Laboratory studies also have not shown how these
  effects lead to autism.

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Scientific AssessmentBiological Mechanisms
Conclusion

• In the absence of experimental or human evidence
  that either the MMR vaccine or vaccines
  containing thimerosal affect metabolic,
  developmental, immune, or other physiological or
  molecular mechanisms that are causally related to
  the development of autism, the committee
  concludes that the hypotheses generated to date
  are theoretical only.

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Significance Assessment

• The committee concludes that because autism can
  be such a devastating condition, any speculation
  that links vaccine and autism means that this is
  a significant issue.

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Recommendations for Public Health Response

• The committee recommends a public health
  response that fully supports an array of vaccine
  safety activities.
  
• The committee recommends that available for
  funding for autism research be channeled to the
  most promising areas.

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Recommendations for Public Health Response
Policy Review

• No policy review of the licensure of the MMR
  vaccine or thimerosal-containing vaccines and or
  of current schedule and recommendations for
  administration of those vaccines.

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Recommendations for Surveillance and
Epidemiological Research

• Use standard and accepted case definitions and
  assessment protocols for ASD
  
• Conduct clinical and epidemiological studies of
  sufficient rigor to identify risk factors and
  biological markers of ASD
  
• Strengthen surveillance of adverse events
• e.g., standardize case definitions of adverse
  events establish guidelines for use of VAERS
  continue use of large linked databases and other
  tools further develop of CISA.

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Recommendations for Surveillance and
Epidemiological Research (cont.)

• Conduct surveillance of ASD as exposure to
  thimerosal declines
  
• Increase efforts to quantify level of prenatal
  and postnatal exposure to thimerosal and other
  forms of mercury in infants, children, and
  pregnant women

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Recommendations for Clinical Studies

• Because chelation therapy has potentially serious
  risks, the committee recommends that it be used
  only in carefully-controlled research settings
  with appropriate oversight by Institutional
  Review Boards protecting the interests of
  children who participate.

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Recommendations for Communication

• Develop programs to increase public participation
  in vaccine safety research and policy decisions
  AND to enhance the skills and willingness of
  scientists and government officials to engage in
  constructive dialogue with the public about
  research findings and their implications for
  policy development.

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Contact Information

• Phone [phone]
• Email imsafety_at_nas.edu
• Website www.iom.edu/imsafety