Effects of California Assembly Bill 2109 in Low Vaccination Rate Counties: Are We Looking at the Right Variables?

California Assembly Bill 2109 (AB2109) was passed in 2012 and restricted the obtainment of personal belief exemptions (PBEs) for vaccination requirements for school-aged children. This study examined changes in up-to-date (UTD) vaccination rates, PBEs, and conditionally accepted students (CASs) at 3 time points. The study also examined the association of PBEs and CASs on county and school immunization rates.

This study utilized 6 academic years of immunization data from all kindergartens in California from 2010-2011 to 2015-2016. The years were selected to include data 2 years prior to the introduction of the bill, 2 years prior to implementation, and 2 years after the new legislation went into effect in 2014. Data were analyzed for changes in variables over time at the state, county, and school levels. A Pearson correlation was performed to assess the association between CAS, PBE, and not-UTD rates in low- and high-UTD counties.

Counties with the highest percentage of unimmunized students have significantly higher mean CAS rates than PBE rates (P < .01 for all years). CASs were found to be more highly correlated with students not-UTD with immunizations than PBEs in all years studied (P < .01 for all years) and with far greater effect size in low-UTD counties (<90% UTD rate). There was a small rise in PBEs and a small reduction in UTD rates after AB2109 was signed but a fall in PBE and CAS rates and a rise in UTD rates postimplementation.

Many California counties have high levels of CASs at the time of kindergarten entry. The extent to which schools require CASs to complete required vaccinations is not known, which could contribute to the pool of undervaccinated students in California. Public health officials should be vigilant to ensure that schools follow up and enforce the completion of vaccines for conditionally admitted students. This study has policy implications due to the fact that it has been revealed that there is a large undervaccinated population remaining relatively unaccounted for in California despite recent efforts.