Nonmedical exemptions to immunization requirements in California: a 16-year longitudinal analysis of trends and associated community factors.

Background: Rates of nonmedical exemptions to kindergarten-entry immunization requirements have increased over the past 2 decades, especially in states that permit philosophical exemptions and/or have easier administrative policies for obtaining nonmedical exemptions. We evaluated trends in school personal belief exemption rates over the period 1994-2009 in California, and associated school and community characteristics.

Methods: We used data on personal belief exemptions from 6392 public and private elementary schools from the California Department of Public Health, as well as census tract and school demographic data. Generalized estimating equations were used to model annual mean increases in personal belief exemption rates, and to identify school and community characteristics associated with personal belief exemption rates.

Results: Over the study period, the average school personal belief exemption rate increased from 0.6% in 1994 to 2.3% in 2009, an average of 9.2% (95% CI: 8.8-9.6%) per year. The average personal belief exemption rate among private schools over the entire study period was 1.77 (95% CI: 1.55-2.01) times that among public schools. The annual rate of increase was slightly higher among private schools (10.1%, 95% CI: 9.1-11.1%) than among public schools (8.8%, 95% CI: 8.4-9.2%). Schools located within census tracts classified as rural had 1.66 (95% CI: 1.26-2.08) times higher personal belief exemption rates than schools located within urban census tracts. Exemption rates were also associated with race, population density, education, and income.

Conclusions: This study confirms concerns about increasing rates of nonmedical exemptions to kindergarten vaccine requirements within the state of California, using data collected over a 16-year period.