More kindergartners in California were up-to-date on their vaccinations in 2017, following three statewide policies, scientists say.
Two stricter laws on vaccine exemptions and a school admission policy, enacted from 2014 to 2016, were associated with a decrease in the rate of kindergartners who were behind on required vaccinations for nine diseases including measles, mumps, pertussis and chicken pox. The rate, which had increased from 7.8 percent in 2000 to 9.8 percent in 2013, dropped to 4.9 percent in 2017, researchers report online July 2 in JAMA.
“The study illustrates that stricter immunization laws improve vaccination rates,” says Jana Shaw, a pediatric infectious disease specialist at the State University of New York Upstate Medical University in Syracuse not involved in the research.
Other states can learn from California’s experience, she says, “and adopt laws that would protect children at schools from vaccine-preventable diseases.”
States can allow children to forgo vaccines for medical reasons or religious or personal beliefs, although which exemptions are permitted depends on the state. A law making it harder to obtain a vaccine exemption based on personal beliefs took effect in California in 2014. Two years later, another law got rid of personal-belief exemptions altogether. And in 2015, the state’s department of health tightened requirements for allowing children who are behind on their immunizations to begin school.
To examine the effect of the three initiatives, researchers analyzed school-entry data for more than 9 million California children from 2000 to 2017. Along with the drop in the rate of kindergartners not caught up on required vaccinations, the chance of two kindergartners behind on vaccinations coming into contact with each other at school fell from 26 percent in 2014 to 4.6 percent in 2017.
There were also fewer schools located in geographic pockets with a high concentration of kindergartners behind on vaccinations: 1,613 schools in 110 areas in 2016–2017, a drop from 2012–2013 when there were 3,026 schools in 124 areas.
These findings suggest that “the risk of a disease outbreak also decreased over the course of the interventions,” says Cassandra Pingali, a public health researcher who worked on the study while at Emory University in Atlanta. Areas that contain many unvaccinated people or those behind on vaccinations can diminish herd immunity, which describes how many people in a population need to be vaccinated to stop a pathogen from spreading (SN Online: 4/15/19).
Because the three measures were implemented over a short period, with some overlap, the researchers were unable to tease out the effect of each policy separately, says Pingali, who is now on a fellowship with the U.S. Centers for Disease Control and Prevention in Atlanta.
The researchers also noted that with the elimination of personal exemptions, the rate of medical exemptions went up, from 0.19 percent in 2013 to 0.73 percent in 2017. That could be because some parents found ways around the personal-exemption ban by instead getting medical exemptions for their children.
As of June 27, there were 1,095 confirmed cases of measles in 28 states this year, making it the country’s biggest outbreak in 27 years, according to the CDC. In May, Maine joined California, West Virginia and Mississippi in permitting exemptions for medical reasons only, a policy then adopted by New York in June. In a narrower change this year, Washington removed the personal belief exemption specifically for the combined measles, mumps and rubella vaccine.