California Senate bill (SB) 277 eliminated the personal belief exemption (PBE) provision from the state's school-entry vaccine mandates prior to the 2016-2017 school year. Previously, vaccine-hesitant parents could acquire a PBE for their child based on philosophical or religious beliefs. Now, the only pathway for an unvaccinated kindergartener to enter a public or private school in California is with a medical exemption (ME), which requires a written statement from a licensed physician describing the medical reasons that immunization is unsafe. 1 Previously, MEs were only granted to children with a contraindication to vaccination; however, SB 277 gave physicians broader discretion to grant MEs for reasons other than a contraindication, including family medical history. 2,3 One concern voiced after the passage of SB 277 was whether vaccine-hesitant parents would seek MEs as replacements for PBEs and would find physicians willing to oblige them. 4 We evaluated the statewide change in MEs in the first year under SB 277 and whether MEs increased in regions with high PBE use prior to its enactment.Methods | We used publicly available data from the California Department of Public Health's yearly Kindergarten Immunization Assessment reports. Each year, all schools are required to submit kindergarten enrollment, vaccination, and exemption data; more than 95% of all kindergarteners are represented in the yearly reports, which include statewide and county-level data. We extracted the statewide ME and PBE percentages for incoming kindergarteners from 1996 to 2016. We calculated and mapped the 1-year change in ME percentage (2015 to 2016) for counties and used Pearson correlation to test whether county-level change in ME percentage was associated with PBE use in the year prior to the implementation of SB 277. We used ArcGIS (Esri), version 10.