The scientists, technologists, and engineers who populate Silicon Valley and the California Bay Area deserve their reputation as innovators, building entire new economies on the strength of brains and imagination. But some of these people don't seem to be vaccinating their children.

A WIRED investigation shows that some children attending day care facilities affiliated with prominent Silicon Valley companies have not been completely vaccinated against preventable infectious diseases. At least, that’s according to a giant database from the California Department of Public Health, which tracks the vaccination rates at day care facilities and preschools in the state. We selected more than 20 large technology and health companies in the Bay Area and researched their day care offerings. Of 12 day care facilities affiliated with tech companies, six—that's half—have below-average vaccination rates, according to the state’s data.

>Six out of 12 facilities WIRED surveyed have a level of measles vaccination too low to provide herd immunity.

And those six have a level of measles vaccination that does not provide the "herd immunity" critical to the spread of the disease. Now, this data has limitations—most critically, it might not be current. But it also suggests an incursion of anti-science, anti-vaccine thinking in one of the smartest regions on Earth.

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Fifteen years ago the Centers for Disease Control declared measles eliminated in the United States. Yet an increasing number of parents now skip their children’s vaccines. A discredited and retracted journal article linking the measles-mumps-rubella vaccine, better known as "MMR," to autism helped spark the anti-vaccine backlash, as did celebrity endorsement of non-scientific positions on the timing, number, and effectiveness of vaccines. In any case, vaccination levels in the US have been declining for a decade and a half; a measles outbreak that began in December at Disneyland has spread to 121 people in 17 states. The CDC hasn’t identified the source of the epidemic, but measles is voraciously contagious, and children under age 5 are at greater risk for complications from the disease—including pneumonia, encephalitis, and death.

Three-quarters of the new cases are in California. The state requires children to be immunized for some infectious diseases to get certain immunizations, but parents can skip their children’s shots for medical or religious reasons, or if they claim a "personal belief exemption," or PBE. In 2000—the year the CDC declared measles a goner—95.4 percent of kids entering kindergarten had received their MMR jabs. Today in California that number is 92.6 percent.

>At one Google day care, only 49 percent of children are completely vaccinated.

Pay close attention to that number. It's critical because of herd immunity—like any drug, in a small number of people vaccines don’t work. So the protective effect on a population only kicks in when a certain portion of the population is vaccinated. That rate for measles is 92 percent. A decade after vaccine rates started declining, that vaccination rate is perilously close to the level at which herd immunity no longer applies.

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Now, here come the caveats: Data is updated infrequently, so low vaccination rates can sometimes reflect out-of-date information. So it’s possible the data's old, or just plain wrong. But we don’t think that's the reason. For one thing, their rates are below the average for the counties in which they’re located.

Let’s get more specific. Take Google: According to the California DPH data, more than 200 children are enrolled at two Google childcare facilities in Silicon Valley. One facility has an overall vaccination rate of 77 percent, and 90 percent got the MMR—straining to reach herd immunity and not quite getting there. Three percent of the families there claim a personal belief exemption. At a nearby Google day care, only 49 percent of children—less than half—are completely vaccinated. Just 68 percent are up to date with their MMRs, which is well below the 92 percent herd immunity threshold. And in Google's home county, Santa Clara, where the vaccination rate average is 88 percent—95.6 for MMR.

But Google has a simple explanation—a representative chalked it up to old data. "In 2013-2014, these two childcare facilities had immunization rates of 98 percent and 81 percent," says a Google spokesperson, emphasizing that immunization is important to the company. "The reported numbers for the current year are lower simply because many parents have not yet provided updated immunization records. We've asked them all to do this, so we can update the figures.”

The numbers are similar at two Santa Clara county facilities associated with networking giant Cisco Systems, where the overall vaccination rates are 72 and 55 percent. Cisco spokeswoman Robyn Blum attributes the company’s low vaccination rates to the age of the children at those facilities. "Cisco childcare facilities care for infants who are under the age of completion for full vaccination series, " says Blum. "Neither Cisco center has children enrolled and not vaccinated due to permanent medical exemption, personal belief exemption, or religious exemption." Julie Kane, a spokesperson for Bright Horizons, a chain of day cares that operates facilities for many corporations, including IBM, says that Big Blue’s Silicon Valley childcare has low rates simply because of the number of infants who are enrolled.

That seems strange to us, though. The California DPH numbers only cover children between 2 and 5 years old, so as we understand it, a large infant population—very young kids ineligible for the MMR, let's say—shouldn't skew the overall rate.

>The rates are more egregious at a Pixar-associated day care. Only 43 percent of children there are immunized.

Nearby, Yahoo’s affiliated facility boasts a 94 percent rate for MMR vaccination.

Across San Francisco Bay in Berkeley, the rates are more egregious at a facility associated with Pixar. Only 43 percent of children there are immunized, with 2.3 percent claiming a personal belief exemption. Just over two-thirds of children there got the MMR. Pixar has yet to return our calls.

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Happily, we found some bright spots. Employees at the biotech companies Gilead Sciences and Genentech, both in San Mateo County, have excellent vaccination rates. Initially we thought this might spin into a distinction between technologists working on computers and scientists working on the rest of the world, but it turns out that day care centers affiliated with Electronics Arts and Oracle also have rates well in the safe zone. Curiously, 2.9 percent of kids at one Genentech-associated facility have a PBE on file, even though their vaccination rate is high.

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You’ll notice a bunch of familiar company names missing from our list. Facebook, Intel, Symantec, eBay, VMware, and Apple are among the companies we checked out that aren’t affiliated with a specific day care centers. Twitter only recently began offering a service to employees, and data for that facility isn’t yet available.

The best news, though, might come from Sacramento. California’s personal belief exemption may be on its way out. In 2012 the state began requiring parents who claim a PBE to receive counseling from a health care professional when refusing shots. And now two California state senators are planning to propose legislation that would repeal the personal belief exemption entirely. That might help bring some of these numbers up.