Association for Public Policy Analysis & Management

Childhood vaccination plays a prominent role in minimizing the incidence of vaccine-preventable disease (VPD). Beyond protecting individual children from VPDs, vaccination has positive externalities because it contains the spread of infection in the general population and contributes to herd immunity. To ensure widespread coverage, states have enacted school immunization mandates whereby proof of vaccination is required to enroll children in school and preschool programs. School immunization mandates have been highly effective in achieving target vaccination rates in the U.S. However, all states allow some form of vaccination exemption.

In general, exemptions fall into two main categories: medical and non-medical exemption. Medical exemptions are granted to children with genuine contraindications to vaccination—when a specific vaccine, or vaccination in general, is deemed to be detrimental to an individual’s health. All states allow for medical exemptions, subject to a written certificate by a licensed physician. Non-medical exemptions allow individuals to refuse vaccination based on deeply held religious beliefs, or for philosophical or personal beliefs that preclude vaccination. While offering non-medical exemptions preserves parents’ autonomy to make medical decisions for their children, misplaced fear over vaccine safety and side effects in recent years has given rise to anti-vaccination sentiment and increased utilization of non-medical exemptions.

The connection between nonmedical exemptions and outbreaks of VPDs is widely established in the literature. However, few studies have looked at the impact of nonmedical exemptions on an intermediate outcome—vaccination coverage. Examining the relationship between the availability of nonmedical exemptions and subsequent coverage is a critical step towards preventing future outbreaks of disease. Therefore, our paper aims to contribute to the literature on childhood vaccination and immunization policy by providing evidence of the causal impact of nonmedical exemptions on immunization coverage for school mandated vaccines.

Our study explores the relationship between non-medical exemptions and vaccination coverage using a recent policy change in California. In 2015, California experienced one of the most severe measles outbreaks in over a decade attributable to vaccine hesitancy. The state responded quickly to the outbreak by removing all non-medical exemptions, effective for the 2016 school year. Employing a unique data set of county-level vaccination and exemption rates at Kindergarten entry, we exploit the policy change in California using a differences-in-differences framework to estimate the impact of the repeal of non-medical exemptions on immunization coverage for school-mandated vaccines.

Relative to a diverse group of control states, our findings indicate that vaccination coverage increased for all required vaccines following the repeal. We also find a significant decline in non-medical exemptions, accompanied by a stark increase in medical waivers in counties that previously had high rates of non-medical exemptions. These results have important public health and policy implications. Our findings indicate that the repeal of non-medical exemptions in California was only partially effective in improving vaccination coverage, and may have led parents to substitute between medical and non-medical exemptions. As a result, the availability and concentration of medical exemptions may increase the vulnerability of certain counties to future outbreaks of disease.