The proportion of California kindergartners with medical exemptions from vaccination tripled after the state eliminated personal belief exemptions, a study has shown.

Furthermore, California counties that previously had the highest rates of personal belief exemptions now have the highest rates of medical exemptions, Paul L. Delamater, PhD, of the University of North Carolina at Chapel Hill, and his associates reported in a research letter in JAMA. Such trends undermine California Senate Bill 277, will “limit [the law’s] long-term benefits, if sustained,” and could lead to outbreaks of vaccine-preventable diseases in the near future, the researchers warned.

Beginning in fall 2016, SB 277 prohibited unvaccinated kindergartners from matriculating at a public or private school in California without a medical exemption from vaccination, having eliminated the personal belief exemption from the state’s school-entry vaccine requirements. But the new law also gave physicians broader discretion to grant the medical exemptions, prompting concerns that “vaccine-hesitant” parents might successfully obtain medical exemptions in lieu of personal belief exemptions. To explore that possibility, the researchers analyzed data from the California state health department on kindergarten enrollment, vaccination, and vaccination exemptions. These data covered about 95% of California kindergartners, Dr. Delamater and his associates noted ( JAMA. 2017;318[9]:863-4 ).

During any given year from 2001 through 2015, between 0.14% and 0.20% of California kindergartners had medical exemptions, the investigators determined. In 2016, this rate soared to 0.51%, a threefold rise from the year before. The findings suggest that some physicians granted medical exemptions to children who had no contraindication to vaccination, contradicting recommendations from the American Academy of Pediatrics, they concluded.

At the county level, rates of medical exemptions strongly correlated with historic rates of personal belief exemptions (P less than .001). Thus, counties with the highest historic rates of personal belief exemptions had the largest increases in rates of medical exemptions in 2016, that is, a change of between –1.00% and 3.38% of kindergartners. Furthermore, vaccination rates among all elementary school-aged children in California are even lower because SB 277 permitted children who previously entered kindergarten with personal belief exemptions to continue attending school without receiving vaccines until seventh grade. “Because the largest increases in [medical exemption] percentage occurred in regions with high past–[personal belief exemption] use, portions of California may remain susceptible to vaccine-preventable disease outbreaks in the near future,” Dr. Delamater and his associates concluded.

The investigators reported having no conflicts of interest.