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.

Thursday, 19th of November 2015

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.

Wilson SE¹ Seo CY¹ Lim GH¹ Fediurek J¹ Crowcroft NS¹ Deeks SL¹.

 

Abstract

BACKGROUND:

Under Ontario legislation for select vaccine-preventable diseases non immunized 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.

INTERPRETATION:

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.