Nonmedical Exemptions From School Immunization Requirements: A Systematic Review

Eileen Wang; Jessica Clymer, BA, BSN; Cecilia Davis-Hayes, BA; Alison Buttenheim, PhD, MBA


Am J Public Health. 2014;104(11):e62-e84. 

In This Article


We designed and report this systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.[12] The protocol was not registered. We identified search terms, inclusion criteria, and exclusion criteria before the literature search. The search terms were exemption* AND (vaccin* OR immuniz*), and we restricted the results to 1997 to 2013 to capture exemption dynamics in the most recent period of vaccine hesitancy and refusal.[13,14] For the study to be included, it had to be an empirical or modeling study that addressed at least 1 of the following topics:

  1. prevalence and trends in exemptions from mandated school-entry vaccines,

  2. predictors or correlates of seeking an exemption (parent level) or granting an exemption (provider, school, or community level),

  3. characteristics and trends in state-level exemption policies and their impact on exemption rates and disease risk, and

  4. epidemiological implications of exemptions.

We excluded studies if they

  1. were not in English;

  2. did not refer to US exemption laws and trends;

  3. did not refer to exemption from school vaccine mandates;

  4. did not refer to personal belief, philosophical, religious, or nonmedical exemptions; or

  5. referred only to the legal or ethical arguments for or against vaccine mandates or exemptions.

We conducted electronic searches in CINAHL, PubMed, and OVID or MEDLINE in consultation with a reference librarian. We found additional studies through citation searches of identified articles and through Table of Contents alerts from Pediatrics, Vaccine, American Journal of Public Health, JAMA Pediatrics, and Health Affairs after our search was conducted. J. C., E. W., and C. D.-H. screened titles and abstracts of articles identified in the initial search for eligibility according to inclusion and exclusion criteria, with no discrepancy in study selection. Studies deemed eligible after the first screen were then assessed in a full-text review using the same inclusion and exclusion criteria. E. W. and J. C. extracted the following elements from included articles: data collection time frame, sample size, study methodology, geographic location, demographics, and key results by topic (prevalence and trends, predictors or correlates of seeking or granting exemptions, characteristics and trends in state-level policies, and epidemiological implications).

After data extraction, we also assessed the articles for quality; because the majority of included articles were observational, we used the Quality Assessment Tool for Systematic Reviews of Observational Studies.[15] This tool covers aspects of external validity, reporting, bias, and confounding; it checks for appropriate sampling methods, reliable and valid measurement of the predictor and outcome variables, an adequate response rate, control for any confounding factors, and appropriate statistical methods. E. W. reviewed each eligible article using this tool; all 44 eligible studies met a medium or high quality standard, and therefore all were included in the review.

E. W. analyzed and qualitatively summarized key results according to the 4 key topics of interest, and A. B. verified them. Some studies' results addressed more than 1 topic and were therefore included in more than 1 category. Within each topic, studies with similar data and results were grouped together and synthesized, and studies with conflicting results were noted.