In 2008, a measles outbreak spread in California. A child whose parents had made an affirmative decision not to vaccinate him brought the disease back from Europe, infecting other children at his doctor’s office and his classmates. The boy’s parents had signed a “personal belief exemption” affidavit stating that some or all of the immunizations were against their beliefs, thereby allowing their son to go unvaccinated before entering kindergarten. California is one of 20 states that allow such exemptions.
The fact that the outbreak spread in a school setting—indicating that other children were also unvaccinated—concerned Robert Wood Johnson Foundation (RWJF) Health & Society Scholar program alumna Alison Buttenheim, PhD, MBA (2009-2011), an assistant professor at the University of Pennsylvania School of Nursing.
“Vaccines are one of the great public health achievements of the last couple of centuries,” Buttenheim says. “They protect us from diseases that used to routinely kill hundreds of thousands of kids in the United States and still kill hundreds of thousands globally. It’s not just important for your child to be vaccinated, it’s important at a population level to have high rates of coverage.”
People who can’t get immunizations because of allergies or compromised immune systems rely on “herd immunity,” the protection they get from a disease when the rest of the population is immunized or immune. If a high number of children are intentionally unvaccinated because of personal belief exemptions, herd immunity is compromised, she explains, giving a disease the chance to spread rapidly.
To gauge the likelihood of future outbreaks, Buttenheim—under the auspices of the RWJF Health & Society Scholars program—and her colleagues assessed how many children in California have received personal belief exemptions, paying particular attention to the grouping of exempted children within schools. The study, coauthored by Malia Jones, BA and Yelena Baras, BA, was published online in the June 14 edition of the American Journal of Public Health.
The researchers looked at data that more than 7,000 public and private schools report to the California Department of Health each year, for some 500,000 kindergarteners. They looked at each of the previous three school years and found that children with one or more personal belief exemptions increased 25 percent in the state from 2008 to 2010. They also found that exempt children tended to aggregate within individual schools, and that a growing number of kindergarteners—both adherent and exempted—were attending schools with potentially risky personal belief exemption rates.
“All of these measures are very clearly increasing over time and some of them quite rapidly,” Buttenheim says.
The researchers also compiled county-specific data to better understand where exempted children are located. In addition to the number of exempt children, they looked at factors that are important for determining where an outbreak could take hold: the likelihood that a child with an exemption will interact with another exempt child (the aggregation index) and the likelihood that an adherent child will interact with an exempt child (the interaction index).
Counties with larger populations predictably had higher numbers of personal belief exemptions, but the highest percentage of children with exemptions were in the smaller counties in the Sierra Nevada Mountain range and in the northwest region of the state. At some schools with the highest rates of personal belief exemptions, more than one in five kindergarteners was exempt.
While rates of immunization at the national level are adequate, “it is likely that herd immunity in smaller localities… may have already been compromised,” the researchers write. Buttenheim hopes that her research team’s county-level results can be used as a prioritizing tool for state policy-makers to intervene in areas with the highest percentage of exemptions.
Changing School Culture
Not every child who is counted as exempted is missing all of the required vaccines. Parents can sign personal belief exemptions for one or more vaccines and have their child partially vaccinated. Some children are also “conditionally accepted” to kindergarten, meaning they are not up to date on their vaccinations but the parent is planning to complete their record in a timely manner.
However, conditional acceptances require additional follow-up from school staff. Based on results from a small study conducted by the California Department of Public Health, Buttenheim hypothesizes that schools may encourage parents to file an exemption rather than grant conditional acceptance and have to follow up later. “It’s a hassle for schools to grant conditional acceptance. We’d like to see it be more of a hassle for parents to get an exemption and to see the conditional acceptance status work as intended.”
“We know from others’ research that states with easier exemption policies have more exemptions, and California is a fairly easy state in which to exempt. Let’s make complying with the mandated vaccines easier than opting out. Make opting in easier than opting out,” she says.
Buttenheim hopes to test several interventions at the school level, including new incentive structures for schools to increase adherence rates. She also thinks the school nurse can play a key role in encouraging parents to get children immunized. “We know everyone is heavily influenced by social norms and pressure,” she explains, and school nurses can set the expectation that children get fully vaccinated. “I think the school nurse can really act as a gatekeeper here, and reset the norm in favor of immunization.”