Vaccine Refusal and Risk of Vaccine Preventable Diseases

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Vaccine Refusal and Risk of Vaccine Preventable
Diseases
Saad B. Omer, MBBS MPH PhD Emory University,
Rollins School of Public Health
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Impact of Vaccines on Infectious DiseasesUnited
States
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Evolution of Immunization Program and Prominence
of Vaccine Safety
Chen, CDC
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School Immunization Requirements in the United
States

• State laws (not federal)
• Major role in low rates of vaccine preventable
  diseases
• Exemptions
• Medical
• Religious
• Personal belief (philosophical) exemptions (21
  states)

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Relative Risk of Measles and Pertussis
inExemptors from School Laws
Measles Pertussis

• CO (1987-98) 22 5.9
• U.S. (1985-1992) 35

Feikin et al. JAMA. 2000 Salmon et al, JAMA.
1999.
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Complexity of Administrative Procedures to Obtain
Exemptions Proportion of Children with
Exemptions
Source Rota et al., AJPH, 2001
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Pertussis (Whooping Cough)
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Associations between State Exemption Policies and
Pertussis Incidence, 1986-2004
Adjusting for allowing parental signature for
school immunization forms, proportion inside
urbanized area, income (11 categories), and
education (7 categories)
Omer et al., JAMA, 2006
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State Policies

• Easy process High exemption rates
• Exemption rates associated with individual risk
  of pertussis measles
• State policies Disease
  incidence

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Model legislation

• AAP (AR Chapter), JHBSPH, AR Med Society
• Precedence of public health interests
• Imposing mandatory requirements in low-risk
  situations
• Ultimate authority to public health agencies

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Non-Medical Exemptions by year1991 - 2003
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Nonmedical Exemptions for States With Religious
Exemptions and With Personal Belief Exemptions
-1991 - 2004
Only Religious Exemptions Permitted
Personal Belief Exemptions Permitted
Exemption Rate
Omer , Pan, Halsey et al., JAMA, 2006
Data updated
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Nonmedical Exemptions by Ease of Exemption 1991
- 2007
Easy Exemption Policy
Medium Exemption Policy
Difficult Exemption Policy
Omer , Pan, Halsey et al., JAMA, 2006
Data updated
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Variability in Vaccine Refusal

• Number of exemptors affects the incidence of
  measles in nonexempt populations
• e.g. school-based outbreaks associated with
  exemption rates
• Within-state variability in implementation of
  exemptions

Feikin et al. 00 Salmon et al., 99 05
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Relative Locations of Pertussis Space-time
Clusters Exemptions Spatial Clusters
Omer , Enger, Moulton et al., 2008
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Locations of schools included in exemption
clusters in California and Massachusetts
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Incidence Rate Ratios (IRR) of Pertussis in
Census Tracts Inside vs. Outside Exemptions
Clusters
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WA State Counties School Entry Exemption
Rates2005-2007
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Vaccine Delay

• Novel vaccine schedules
• Consequences not studied in detail
• Risk of vaccine preventable diseases is not
  constant across childhood
• Vaccine delays may leave young children
  vulnerable
• Potential exacerbation of health inequities

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MMWR, 2008
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MMWR, 2008
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Measles Outbreaks in England Wales
MMWR, 2008
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Risk vs. Benefit Calculus for MeaslesAn example
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Mechanisms to Ensure Vaccine Safety

• Animal testing
• Pre-licensure Clinical (Human) Trials
• Phases I, II, III
• Post-marketing Surveillance
• Phase IV studies, VAERS, CISA, VSD

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Institute of Medicine

• Established in 1970
• Congressionally chartered independent
  organization
• Science-based advice on biomedical science,
  medicine, and health issues
• Represents mainstream expert opinion

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IOM Immunization Safety Review on Vaccine and
Autism

• the body of epidemiological evidence favors
  rejection of a causal relationship between the
  MMR vaccine and autismthe body of
  epidemiological evidence favors rejection of a
  causal relationship between thimerosal-containing
  vaccines and autism.

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Thank You!
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