from immunizations, according to Paul L. Delamater, PhD, of the University of North Carolina at Chapel Hill, and associates.
The investigators focused on vaccination data collected from 2015 – the last year before the passage of SB 277 – to 2017. They also analyzed county-level data collected from 2000 to 2014 to assess demographic behavior. In 2015, the rate of nonvaccination was 7.15%, decreasing to 4.42% in 2016. This decrease was almost entirely caused by a reduction in the rate of conditional entrants, which fell from 4.43% to 1.91%, and in personal belief exceptions, which fell from 2.37% to 0.56%.
While the rates of conditional entrants and personal belief exceptions continued to fall in 2017, other mechanisms allowed the overall rate of kindergarteners not fully up to date on their vaccines to jump to 4.87%. This was fueled by a slight increase in medical exceptions (from 0.51% in 2016 to 0.73% in 2017), and a significant increase in children who were overdue or exempt, which both increased from 0 in 2014 to over 1% by 2017.
“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,” the investigators reported in Pediatrics (2019, May 21 doi: 10.1542/peds.2018-3301.
One coauthor reported receiving research and consulting support from Pfizer, Merck, and Walgreens; another reported receiving research support from Pfizer, Merck, GlaxoSmithKline, Sanofi Pasteur, Protein Science (now Sanofi Pasteur), Dynavax, and MedImmune.