The Association Between School Immunization Non-medical Exemptions and Pertussis Incidence: A Geographic Clustering and Transmission Model Approach Open Access

Chuo, Ching-Yi (2012)

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School entrance immunization requirement has been an important strategy in
preventing vaccine preventable diseases among school-aged children in the United
States. 48 states allow for personal beliefs vaccination exemptions which pose threats
of disease transmission in the population. Our research, based on non-medical vaccine
exemption and pertussis incidence data from California, attempted to establish
association between exemptions and vaccine preventable disease transmission on both
temporal and spatial scales.
We received 84,721 geo-coded records from kindergarten on non-medical
exemption from 1994 to 2003. 5695 under age 18 pertussis cases information from
year 2000 to 2004 were provided by the California Department of Public Health. We
accumulated the records into 7049 census tracts as our study individual. Kulldorff's
scan statistics were applied for temporal, spatial cluster identifying. Descriptive
analysis on demographic factors related to both exemption and pertussis clusters was
performed. We applied Poisson regression model for testing the association between
exemption clusters and pertussis. We also construct SIR disease transmission model
with force of infection accounting for exemption clustering risks. Results of model
simulation are compared with observed pertussis on the spatial scale
We identified 56 non-medical vaccine exemption clusters and 8 pertussis
incidence clusters. Both exemption and pertussis clusters are associated with higher
percentage of white ethnicity, lower under 18 population, and lower poverty
percentage (all P<0.001). Our Poisson model on exemption clusters to incidence of
pertussis controlling for demographics yields RR:1.19, 95% CI (1.04, 1.21).
Stimulated results from spatial cluster SIR model are matched with observed pertussis
cases (R2=0.15) and pertussis cluster (R2=0.21)
Our findings suggested that vaccine exemption clusters are associated with the
risk of pertussis outbreaks in California.

Table of Contents

Background & literature review p1

Introduction p9

Methods p11

Results p17

Discussion p21

Reference p24

Tables and figures p27

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