In the past few years California has gained ground in its fight to protect children from infectious diseases. But new data released this week shows that the state’s vaccination rate declined for the second year in a row.

Last fall 94.8 percent of California kindergartners had received all their shots, down from 95.6 in 2016-2017. That drop may look small, but California has about as many kindergartners as Wyoming has people. The most recent figures show that California now falls below the Centers for Disease Control and Prevention’s recommended vaccination rate of 95 percent, considered necessary to protect a community from disease outbreaks through herd immunity. Those numbers also obscure big differences in vaccination rates from one zip code to another, from as low as 19 percent in one community in northern Los Angeles County to as high as 99 percent in Watsonville, a farm town in Santa Cruz County.

Four years ago, following a measles outbreak in Southern California that began at Disneyland, California passed Senate Bill 277, a law that eliminated parents’ ability to opt out of mandated vaccinations for their kids based on personal beliefs. At first, the law seemed to be working. When it was passed, 2.4 percent of kindergartners in California weren’t vaccinated because of a personal belief exemption; today, that figure is zero.

But children can also skip vaccinations if they receive a permanent or temporary medical exemption from a doctor; these are typically given to children who have health conditions, like immune system disorders, that contra-indicate vaccination. Five years ago, just 0.2 percent of California students received a permanent medical exemption, while 2.5 percent claimed a personal belief exemption, or PBE. Since the PBE’s elimination, permanent medical exemption (PME) rates have begun to climb, from 0.7 percent to 0.9 percent for the past year.

California Department of Public Health data suggests that communities in which PBEs were popular in the past may now be obtaining PMEs. As Barbara Feder Ostrov reported in Kaiser Health News earlier this spring, many schools that previously claimed the highest PBE rates now have high PME rates.

New data released this week backs up this analysis. The California schools with the highest exemption rates today—we’re talking rates of 40, 50, even 64 percent of a group of a few dozen kindergartners—had PME rates of zero five years ago. So five years ago, kindergarten classes at these schools had no children whose health was compromised to the degree that they could not medically handle immunizations. At the time, those same schools claimed very high PBE rates—ranging from 35 percent to 87 percent. About half of the schools with the highest PME rates are Waldorf schools. (Waldorf schools follow an educational model developed by Rudolf Steiner and Emil Molt that emphasizes bringing out each child’s individual potential in a way that serves humanity.)

Take Yuba River Charter, a Waldorf-affiliated school in Grass Valley, California. (Grass Valley is northeast of Sacramento, in a county where 10.6 percent of kids have a PME and only 80.3 percent are fully vaccinated.) In 2013, more than two-thirds of Yuba River Charter’s kindergartners claimed personal belief exemptions. Today, that figure is zero. But just 36 percent of students at the school are vaccinated, with the remainder claiming a permanent medical exemption. (Administrators did not respond to a request for comment.)