title: Trends in medical and nonmedical immunization exemptions to measles-containing vaccine in Ontario: an annual cross-sectional assessment of students from school years 2002/03 to 2012/13.
abstract: BACKGROUND
  Under Ontario legislation, for select vaccine-preventable diseases nonimmunized or under-immunized students must undergo vaccination or provide a statement of exemption, or risk suspension from school. At the time of this assessment, these diseases included measles, mumps, rubella, diphtheria, tetanus and polio.
  
  
  METHODS
  Exemptions data for the school years 2002/03 to 2012/13 were obtained from the Immunization Records Information System used in Ontario. Temporal trends were expressed for 7- and 17-year-old students by exemption classification (medical, prior immunity, religious or conscientious belief, total) at the provincial level, by school year and by birth cohort. Regional analysis was conducted for the 2012/13 school year. A temporal trend analysis of exemptions for measles-containing vaccines was performed by using a Poisson distribution with a 2-sided test (α = 5%).
  
  
  RESULTS
  For both 7- and 17-year-old students, religious or conscientious exemptions for measles-containing vaccines significantly increased over the study period (p < 0.001 in both age groups), whereas medical exemptions decreased (p < 0.001 in both age groups). The trends were reproduced when examined by birth cohort. The percentage of Ontario students with any exemption classification (total exemptions) remained low (< 2.5%) during the study period, although considerable geographic variation was noted.
  
  
  CONCLUSIONS
  Ontario data suggest that nonmedical exemptions have increased during the last 11 years, consistent with trends reported elsewhere. The trend toward increasing religious or conscientious exemptions coupled with declining medical exemptions explains why total exemptions have remained stable or decreased at the provincial level. The prominent geographic variability in exemptions suggests that targeted interventions may be suitable for consideration.
authors.affiliation: Public Health Ontario (Wilson, Seo, Lim, Fediurek, Crowcroft, Deeks), Toronto, Ont.; Dalla Lana School of Public Health (Wilson, Crowcroft, Deeks); Department of Laboratory Medicine and Pathobiology (Crowcroft), University of Toronto, Toronto, Ont.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Wilson
authors.affiliation: Public Health Ontario (Wilson, Seo, Lim, Fediurek, Crowcroft, Deeks), Toronto, Ont.; Dalla Lana School of Public Health (Wilson, Crowcroft, Deeks); Department of Laboratory Medicine and Pathobiology (Crowcroft), University of Toronto, Toronto, Ont.
authors.forename: Chi Yon
authors.initials: CY
authors.lastname: Seo
authors.affiliation: Public Health Ontario (Wilson, Seo, Lim, Fediurek, Crowcroft, Deeks), Toronto, Ont.; Dalla Lana School of Public Health (Wilson, Crowcroft, Deeks); Department of Laboratory Medicine and Pathobiology (Crowcroft), University of Toronto, Toronto, Ont.
authors.forename: Gillian H
authors.initials: GH
authors.lastname: Lim
authors.affiliation: Public Health Ontario (Wilson, Seo, Lim, Fediurek, Crowcroft, Deeks), Toronto, Ont.; Dalla Lana School of Public Health (Wilson, Crowcroft, Deeks); Department of Laboratory Medicine and Pathobiology (Crowcroft), University of Toronto, Toronto, Ont.
authors.forename: Jill
authors.initials: J
authors.lastname: Fediurek
authors.affiliation: Public Health Ontario (Wilson, Seo, Lim, Fediurek, Crowcroft, Deeks), Toronto, Ont.; Dalla Lana School of Public Health (Wilson, Crowcroft, Deeks); Department of Laboratory Medicine and Pathobiology (Crowcroft), University of Toronto, Toronto, Ont.
authors.forename: Natasha S
authors.initials: NS
authors.lastname: Crowcroft
authors.affiliation: Public Health Ontario (Wilson, Seo, Lim, Fediurek, Crowcroft, Deeks), Toronto, Ont.; Dalla Lana School of Public Health (Wilson, Crowcroft, Deeks); Department of Laboratory Medicine and Pathobiology (Crowcroft), University of Toronto, Toronto, Ont.
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Deeks