The Emergence of Spatial Clustering in Medical Vaccine Exemptions Following California Senate Bill 277, 2015–2018

Abstract

Objectives. To understand how the elimination of nonmedical vaccine exemptions through California Senate Bill 277 (SB277) may have resulted in increased spatial clustering of medical exemptions. Methods. We used spatial scan statistics and negative binomial regression models to examine spatial clustering in medical vaccine exemptions in California kindergartens from 2015 to 2018. Results. Spatial clustering of medical exemptions across schools emerged following SB277. Clusters were located in similar geographic areas to previous clusters of nonmedical vaccine exemptions, suggesting a spatial association between high nonmedical exemption prevalence and increasing rates of medical exemptions. Regression results confirmed this positive association at the local level. The sociodemographic characteristics of the neighborhoods in which schools were located explained some, but not all, of the positive spatial associations between exemptions before and after SB277. Conclusions. Elimination of nonmedical vaccine exemptions via SB277 may have prompted some parents to instead seek medical exemptions to required school vaccines. The spatial association of these 2 types of exemptions has implications for maintaining pockets of low vaccine compliance and increased disease transmission.

Opting Out: Individualism and Vaccine Refusal in Pockets of Socioeconomic Homogeneity

“…Moreover, even in states that do restrict or eliminate PBEs, parents who are resolved to opt out seem to find ways of doing so. A recent study of vaccine exemptions in California revealed that SB277 did eliminate clusters of PBEs, but permanent medical exemptions (PMEs) rose precipitously after the law went into effect, and PME clusters quickly emerged in the same settings where PBEs were previously high (Gromis and Liu 2020). Other solutions are needed.…”

“…From a public health perspective, the most concerning issue is that vaccine exemptions cluster in particular communities and schools (Brennan et al 2017; Carrel and Bitterman 2015; Delamater et al 2018; Lieu et al 2015; Omer et al 2008). Recent research indicates these clusters persist even when states minimize access to exemptions through stricter vaccination policies (Gromis and Liu 2020). Epidemiologists warn that these pockets of low vaccination are like holes in the protective wall of community health, which weaken herd immunity to infectious diseases and put non-vaccinated individuals and entire communities at risk (Feiken et al 2000; Omer et al 2008; Omer et al 2009).…”

“… 2. SB277 was passed in 2015 and took effect in 2016. Although California no longer accepts PBEs, analyses of data prior to passage of SB277 could inform efforts to combat medical exemptions in California (Gromis and Liu 2020) and should be helpful to the dozens of other states currently debating vaccine policy. …”

The landscape of childhood vaccine exemptions in the United States

“…In all states, medical exemptions from immunizations can be obtained for conditions such as those resulting in immunosuppression or in cases of known adverse reaction to past immunizations. These exemptions have traditionally remained at levels low enough to not represent a threat to herd immunity, although recent dynamics such as that observed in California may change this assessment in the future [4][5][6] . Most other states offer religious exemptions, in which individuals cite personal religious beliefs that preclude vaccination, while others allow philosophical exemptions, which encompasses any personal belief against receiving a vaccination.…”

The landscape of childhood vaccine exemptions in the United States

“…In all states, medical exemptions from immunizations can be obtained for conditions such as those resulting in immuno-suppresion or in cases of known adverse reaction to past immunizations. These exemptions have traditionally remained at levels low enough to not represent a threat to herd immunity, although recent dynamics such as that observed in California may change this assessment in the future [4, 5, 6]. Most other states offer religious exemptions, in which individuals cite personal religious beliefs that preclude vaccination, while others allow philosophical exemptions, which encompasses any personal belief against receiving a vaccination.…”