From the Journals

Legislative, educational interventions influenced vaccine status of California kindergartners



After California lawmakers implemented policies to limit and eventually eliminate nonmedical exemptions for childhood vaccinations, the proportion of kindergartners who were not up to date for recommended vaccinations fell from 10% in 2013 to 5% in 2017.

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At the same time, the percentage chance for within-school contact among California kindergartners without up-to-date vaccination status decreased from 26% in 2014 to 5% in 2017.

The findings come from an observational study that used cross-sectional school-entry data from 2000 to 2017 to calculate the rates of kindergartners attending California schools who were not up to date on required vaccinations.

“Large-scale vaccination programs that included school-entry mandates have been essential to maintaining high levels of immunization coverage and low rates of vaccine-preventable diseases,” researchers led by S. Cassandra Pingali, MPH, MS, wrote in JAMA. “However, an increasing number of parents are not vaccinating their children over concerns about potential adverse effects. These parental actions threaten the herd immunity established by decades of high vaccine uptake and increase the potential for disease outbreaks.”

Ms. Pingali, of the department of epidemiology at Emory University, Atlanta, and colleagues conducted an observational analysis of California kindergartners who were not up to date on one or more of the required vaccinations during the course of three interventions implemented in the state. The first was Assembly Bill 2109 (AB 2109), which was passed in 2014. It required parents to show proof they had discussed the risks of not vaccinating their children with a health care practitioner before they obtained a personal belief exemption. The second intervention was a campaign carried out in 2015 by the California Department of Public Health and local health departments, designed to educate school staff on the proper application of the conditional admission criteria, which allowed students additional time to catch up on vaccination. The third intervention was the implementation of Senate bill 277 (SB 277), which banned all personal belief exemptions.

Between 2000 and 2017, the researchers reported that the yearly mean kindergarten enrollment in California was 517,962 and the mean number of schools was 7,278. Over this time, the yearly rate of students without up-to-date vaccination status rose from 8% during 2000 to 10% during 2013, before decreasing to 5% during 2017. Ms. Pingali and associates also found that average percentage chance of any within-school contact for a student without up-to-date vaccination status with another student with the same status was 19% during 2000, and increased steadily to 26% during 2014, the first year of AB 2109. The values decreased to 3% (the first year of SB 277), before increasing slightly to 5% during 2017.

“Across the interventions, the percentage of kindergartners attending schools with an up-to-date vaccination status percentage that was greater than the herd immunity threshold also increased for various vaccine-preventable diseases,” the researchers wrote. “Overall, the results suggest that the risk of disease outbreak via potential contact among susceptible children decreased over the course of the interventions.”

The way Matthew M. Davis, MD and Seema K. Shah, JD, see it, the current outbreak of measles in the United States is rooted in the failure of parents to vaccinate their children against the disease based on their beliefs rather than medical contraindications.

“The public health implications of such decisions are amplified because parents who share belief systems about childhood vaccinations tend to congregate socially and residentially, thereby forming clusters of unvaccinated children who are at elevated health risks when exposed to vaccine-preventable diseases,” the authors wrote in an accompanying editorial.

While the study reported by Pingali et al. did not measure actual outbreaks of disease, “reductions in children’s risk of contracting measles are a promising outcome in California resulting from policy changes,” wrote Dr. Davis and Ms. Shah, both of Northwestern University, Chicago (JAMA. 2019;322[1]:33-4). “Yet, because of the ease of domestic and international travel, the mobile nature of young families, and the inability of all states to implement this approach, changes made in each state for nonmedical exemptions may not ensure sufficiently high protection against measles for children across all jurisdictions in the United States. Although states have historically made their own decisions about vaccination exemptions linked to day care or school entry because states exercise primary authority over educational matters, childhood vaccination is a national matter in many respects.”

The best way to remedy the current system failure regarding measles vaccination, they continued, may be to adopt a unified national approach to prohibit nonmedical exemptions. They pointed to the fact that the United States previously achieved virtual eradication of measles as recently as 2000. “Following that achievement, state-level policy changes relaxed immunization requirements and set the stage for progressively larger outbreaks in the United States in recent years. Such system failures result when the products, processes, and people (including the public) that comprise systems do not function or behave in ways that protect health optimally.”

The study was supported by a grant from the National Institutes of Health. One coauthor reported having received consulting fees from Merck and grants from Pfizer and Walgreens. Another reported receiving grants from Pfizer, Merck, GlaxoSmithKline, Sanofi Pasteur, Protein Science, Dynavax, and MedImmune. The remaining coauthors reported no relevant financial disclosures.

The editorialists reported having no financial disclosures.

SOURCE: Pingali SC et al. JAMA. 2019 Jul 2. doi: 10.1001/jama.2019.7924.

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