Assessment of Exemptions from Vaccination in California, 2015–2027

Background

In 2015, California passed Senate Bill 277 (SB277) banning nonmedical exemptions from school-entry vaccine mandates. However, some provisions limit SB277’s effectiveness, including “grandfathering” pre-SB277 nonmedical exemptions, exempting homeschooled children and those not in classroom-based environments from vaccine requirements, and relaxing allowable medical exemption criteria (1). In SB277’s first three years, medical exemptions and students not up-to-date on vaccination who were exempt from requirements increased (1).

Objective

We estimated the percent of California schoolchildren with an exemption from vaccination for 2015–2027 under three potential scenarios.

Methods and Findings

We used publicly-available kindergarten and seventh grade vaccination and enrollment data from the California Department of Public Health (CDPH) for 2009–2018 and projected kindergarten enrollment data for 2019–2027 from the California Department of Education. We estimated the exemption status of all California schoolchildren (grades K-12) each year for 2015–2027 using a grade-cohort approach (e.g., kindergarteners in 2015 become first graders in 2016) (2). We implemented three scenarios. The base scenario assumes that current exemption use will continue. The second scenario estimates the potential impact of Senate Bill 276 (SB276), which adds increased scrutiny to medical exemptions (3). The third scenario is a hypothetical in which SB277 was not implemented.

Details of the exemptions for each scenario are in Table 1. We assumed children with pre-SB277 nonmedical exemptions would retain them until seventh grade or graduation (as allowed by SB277) and that students with medical exemptions and those exempt from requirements status would remain so as they advanced through school. In the SB276 scenario, we assumed it would become effective in 2020; based on a CDPH analysis, (3) we assumed only 0.2% of children could obtain valid medical exemptions under SB276. In the No SB277 scenario, we used the 2014–2015 average nonmedical exemption rate beginning in 2016 to account for Assembly Bill 2109, which reduced the nonmedical exemption rate from its pre-2014 level (4).

Table 1.

Data used for nonmedical exemptions, medical exemptions, and exempt from requirements for kindergarteners and seventh graders in each scenario.

	Base*		SB276+		No SB277$
	20152−2018	2019−2027	2015−2018	2019−2027	2015−2018	2019−2027
Nonmedical Exemptions	Observed	0%	Observed	0%	Average of 2014−2015	Average of 2014−2015
Medical Exemptions	Observed	2018 rate	Observed	2019 (2018 rate) 2020−2027 (0.2%)	Average of 2009−2018	Average of 2009−2018
Exempt from Requirements	Observed	2018 rate	Observed	2018 rate	0%	0%

^*We assumed students with pre-SB277 nonmedical exemptions would retain them until reaching seventh grade or graduation. Students were assigned a 0% nonmedical exemption rate after 2017. The most recent rates of medical exemptions and exempt from requirements for kindergarteners (0.87% and 1.50%, respectively) and seventh graders (0.42% and 0.88%, respectively) were used to estimate the number of students with either exemption type entering those grades after 2018.

⁺We assumed SB276 would be implemented in 2020; for 2019, we used the medical exemption rates in 2018. All medical exemptions obtained prior to 2020 would be “grandfathered,” per the most recent modification of SB276. For students exempt from requirements, we used current rates for future years in this scenario.

^$We used the 2014–2015 average nonmedical exemption rate for kindergarteners (2.46%) and seventh graders (1.87%) after 2015 because Assembly Bill 2109 reduced the nonmedical exemption rate from its pre-2014 level (4). For medical exemptions, the 10-year average rate prior to SB277 was used for kindergarteners (0.18%) and seventh graders (0.16%) entering those grades after 2015. Students exempt from requirements were not included because this provision was created by SB277

In the base scenario, the percentage of schoolchildren with any exemption is expected to drop 0.72% from a pre-SB277 level of 2.59%, stabilizing at 1.87%. In the SB276 scenario, the percentage with any exemption would decrease from 2.19% in 2018 to 1.41%. In the No SB277 scenario, the percentage with any exemption would have started decreasing in 2018 and stabilized at 2.36% in 2021, a reduction of 0.21% from 2015. Figure 1 shows the detailed estimates from the three scenarios.

Figure 1. Predicted percent of all schoolchildren exempt from vaccination in California, 2015 to 2027, under the base scenario, the SB276 scenario, and the No SB277 scenario.

The solid line is the sum of all exempted students in the scenarios.

Discussion

If current rates of medical exemptions and students who are exempt from requirements persist, the overall exemption rate in California schools will stabilize at 1.87%, a relatively modest decrease from the 2.59% (pre-SB277) and only 0.49% less than the No SB277 scenario estimate. SB277’s provision exempting some children from vaccination requirements based on educational setting essentially created an alternate exemption option for vaccine-hesitant parents willing to educate their children in these settings. Although not up-to-date children in non-classroom environments will have comparatively less exposure to other children, they interact with others in broader community contexts and remain at risk during a vaccine-preventable disease outbreak (5).

Since SB277’s implementation, the medical exemption rate in California increased dramatically, prompting SB276. CDPH estimated that medical exemptions could be reduced to 0.2% of schoolchildren; however, whether this level of reduction is achievable given last-minute modifications to SB276 is unknown. Further, whether a 0.70% long-term reduction in exempted students justifies the additional resources required to scrutinize medical exemptions has not been assessed and deserves further examination.

Our study has limitations. The grade cohort model assumes the size and exemption status of each cohort is static as students advance through grades. The scenarios we evaluated represent a fraction of the potential future scenarios, which could include changes in vaccine-related behaviors or other legislative actions. Further, while our scenarios are data-driven, they do contain assumptions affecting our estimates; however, all predictions are limited in this manner.

A number of states have recently passed or are considering legislation banning nonmedical exemptions. We demonstrate how these efforts can be mitigated by persistent vaccine hesitancy and the availability of alternate pathways to avoid vaccination. In California, SB277 could have a relatively moderate impact on exemptions, especially if no further legislative action occurs and current trends continue.