Effect of Eliminating Nonmedical Immunization Exemptions in California

A nurse administering a vaccine
A nurse administering a vaccine
Although the percentage of up-to-date vaccinations among incoming kindergarteners increased after implementation of the 2016 senate bill, which eliminated nonmedical immunization exemptions, evidence for a replacement effect was found.

In 2016, California became the first state in almost 30 years to eliminate nonmedical immunization exemptions for schoolchildren with Senate Bill 277 (SB277), and although the percentage of up-to-date vaccinations among incoming kindergarteners increased after implementation, evidence for a replacement effect was found, according to a study published in Pediatrics.

For this study, researchers analyzed the composition and magnitude of the kindergarten population not up to date on vaccinations pre- and post-implementation of SB277 with the objective of determining the effect on the percentage of kindergarteners not up to date, and also if the implementation of the new law affected geographic patterns of vaccine refusal.

In the first year after SB277 implementation, the percentage of incoming kindergartners not up to date on vaccinations decreased from 7.15% to 4.42%, while the conditional entrance rate fell from 4.43% to 1.91%, and personal belief exemptions decreased from 2.37% to 0.56%. However, researchers noted a 0.8% and 0.82% increases in combined replacement and overdue mechanisms. The percentage of not-up-to-date kindergarteners increased by 0.45% in the second year post-implementation, despite additional reductions in personal belief exemptions and conditional entrants. Correlational analysis revealed that after the law’s implementation, geographic patterns of vaccine refusal did persist.

Researchers expressed concern regarding the fact that post-implementation of SB277, medical exemptions have increased 4-fold compared with pre-implementation. They concluded, “Although the law was successful in reducing the number of students with personal belief exemptions, our analysis reveals that a replacement effect may have stifled a larger increase in students entering kindergarten who are up to date on vaccination…Given these findings, policymakers should consider the various options available to increase vaccination coverage or strategies to minimize potential unintended consequences of eliminating nonmedical exemptions such as the replacement effect observed in California.”

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Delamater PL, Pingali SC, Buttenheim AM, Salmon DA, Klein NP, Omer SB. Elimination of nonmedical immunization exemptions in California and school-entry vaccine status [published online May 21, 2019]. Pediatrics. doi: 10.1542/peds.2018-3301