Several weeks after the school year started last fall, and months before the recent measles outbreak, Jill Vollbrecht, an endocrinologist and Children’s House parent of three children ages 4 through 9, read a disturbing report by a local news outlet, the Traverse Ticker. She discovered that between 2008 and 2014, waiver rates—the percentage of those declining vaccinations for both medical and personal reasons—had climbed from 6 percent to 11 percent in Grand Traverse County, which encompasses the school. Moreover, it was now as high as 19 percent in nearby Leelanau County. Even more alarming to her at the time, Michigan health records showed that waiver rates had spiked among local Montessori students compared with other public and private schools within the state. The report showed that nearly a fourth—23 percent—of families at The Children’s House were opting their kids out of vaccinations. "I’m not a family practitioner or an infectious disease specialist, but these numbers set off alarm bells for me," Vollbrecht said. "All physicians have the common goal of wanting to keep our kids and our communities safe, and we have a core understanding about science and herd immunity."

Vaccines only work if enough people in a community are vaccinated—what Vollbrecht referred to as herd immunity. As Biss writes in her book, vaccines are a kind of immunity banking, something an individual may need at a future point in their life: "When enough people are vaccinated, viruses have trouble moving from host to host and cease to spread, sparing both the unvaccinated and those in whom the vaccination has not produced immunity." Researchers have found that, for vaccines to work, 92 percent or more of a population must be immunized against the disease. For highly contagious viruses, it takes 95 percent to protect the entire community.

By either measure, both Grand Traverse County and The Children’s House appeared to have dangerously high exemption rates. At the school in particular, the risk of losing herd immunity was disconcerting because it enrolls babies as young as 3 months old—infants who still aren’t fully vaccinated and rely on the rest of the school to shield them from outbreaks that can be life threatening for young children. In fact, earlier this week, the Los Angeles Times reported that a months-old baby who was too young for vaccinations contracted measles at daycare, forcing the subsequent quarantine of 14 infants enrolled at the same center, which is located on Santa Monica High School’s campus.

So, after seeing the waiver rates this fall, Vollbrecht and a fellow parent and physician, Daniel Flewelling (whose 2-year-old also attends The Children’s House), contacted the school’s head to determine why so many parents were opting out of vaccines and how they could change the admissions policy as quickly as possible. In their view, the state certainly wasn’t helping. According to an MLive analysis of health data, Michigan had made it so easy to sign a waiver that, last December, nearly 45 percent of its residents lived in counties that were at risk of disease outbreaks. And the threat to Traverse City’s children wasn’t merely theoretical. Just a month earlier, the county health department confirmed 22 cases of pertussis, what’s commonly called whooping cough, and even had to temporarily close one of its K-12 charter schools, Grand Traverse Academy. In response, Michigan recently bolstered its policy for daycare centers and licensed schools, requiring parents who refuse vaccinations because of personal beliefs to have their waivers certified by the local health department. In other words, the updated policy means that exemptions are now more than a "check-the-box" formality.