Associations of Statewide Legislative and Administrative Interventions With Vaccination Status Among Kindergartners in California

Importance: California implemented 3 interventions to increase uptake of vaccines. In 2014, Assembly bill 2109 tightened requirements for obtaining a personal belief exemption. A 2015 campaign provided educational materials to school staff on the proper application of conditional admission for kindergartners who were not up to date on required vaccinations. In 2016, Senate bill 277 eliminated personal belief exemptions. Prior research has not evaluated these 3 interventions together with regard to the vaccination status of students.

Objective: To assess the changes in the yearly rates of kindergartners who were not up to date on required vaccinations who were entering school during the period of the interventions, by focusing on geographic clustering and the potential contacts of these kindergartners.

Design, Setting, And Participants: Observational study that used cross-sectional school-entry data from 2000-2017 to calculate the rates of kindergartners attending California schools who were not up to date on required vaccinations.

Exposures: Assembly bill 2109, a conditional admission education program, and Senate bill 277.

Main Outcomes And Measures: The primary outcome was the yearly rate of kindergartners without up-to-date vaccination status. The secondary outcomes were (1) the modified aggregation index, which was used to assess the potential within-school contacts among kindergartners without up-to-date vaccination status, (2) the number of geographic clusters of schools with rates for kindergartners without up-to-date vaccination status that were higher than the rates for schools located outside the cluster, and (3) the number of schools located inside the geographic clusters.

Results: In California between 2000 and 2017, 9 323 315 children started attending kindergarten and 721 593 were not up to date on required vaccinations. Prior to the interventions, the statewide rate of kindergartners without up-to-date status for required vaccinations increased from 7.80% during 2000 to 9.84% during 2013 and then decreased after the interventions to 4.87% during 2017. The percentage chance for within-school contact among kindergartners without up-to-date vaccination status decreased from 26.02% during 2014 to 4.56% (95% CI, 4.21%-4.99%) during 2017. During 2012-2013, there were 124 clusters that contained 3026 schools with high rates of kindergartners without up-to-date vaccination status. During 2014-2015, there were 93 clusters that contained 2290 schools with high rates of kindergartners without up-to-date vaccination status. During 2016-2017, there were 110 clusters that contained 1613 (95% CI, 1565-1691) schools.

Conclusions And Relevance: In California, statewide legislative and educational interventions were associated with a decrease in the yearly rates of kindergartners without up-to-date vaccination status. These interventions also were associated with reductions in the number of schools inside the clusters with high rates of kindergartners without up-to-date vaccination status and the potential for contact among these kindergartners.