In the midst of a measles outbreak stretching from Portland to King County, Washington legislators introduced a bill to end personal exemptions from vaccines, which are otherwise required to attend day cares as well as both public and private schools. This bill was introduced by Rep. Paul Harris of Clark County—where at least 35 people, nearly all of them unvaccinated, have been diagnosed with measles—and it only applies to the measles, mumps, and rubella vaccines.

Currently, parents can opt their kids out of receiving these vaccines if they have religious or philosophical objections, and the number of people seeking these exemptions has been increasing for years. In Clark County, for instance, the vaccination rate for the kindergarteners went from 91.4 percent in 2005 to 76.5 percent in 2018.

The demographics of people seeking these exemptions has changed as well. Vaccines used to be something that a small number of religious groups opposed. Today, however, almost no religions object to vaccines. Instead, the objections more often come from secular people who’ve encountered anti-vax skepticism either in pop culture (for instance, Dr. Oz) or online.

Highly liberal communities like Vashon Island and Waldorf Schools, for instance, often have lower vaccination rates than the state average. At a Waldorf School in the famously progressive town of Asheville, North Carolina, for instance, almost 70 percent of parents refuse to vaccinate their children, and nearly a quarter of the school children contracted chicken pox, also a completely preventable illness, last year.

According to doctors and public health experts, the science behind vaccines has long been settled: Vaccines are one of the safest ways to prevent infectious disease and have vastly lowered mortality rates across the world. And yet, plenty of people remain unconvinced. Larry Cook, for instance, a self-described "advocate for natural living," runs the website StopMandatoryVaccination.com, which posts heartbreaking—though unverified—stories about kids being harmed, or even killed, from vaccines.

Cook lives in California, a state that ended personal exemptions in 2015, but he’s getting involved in the fight over vaccine exemptions in Washington state. This week, he started a $6000 fundraiser to buy Facebook advertising specifically targeting women in Washington state.

“The goal here is to help parents start to question the safety and efficacy of vaccines which will in turn help them realize why vaccine mandates could be problematic for their children,” the fundraiser’s website reads. “We want these parents who are on the fence to become ACTIVISTS in Washington State.” After just a day, the fundraiser was nearly halfway to full funding.

Cook, who says he’s a Washington native, has vocal allies in the area. Bernadette Pajer, the head of Informed Choice Washington and the mother of a 15-year-old son who she says suffers from a “vaccine injury,” has devoted much of her life in recent years to fighting mandatory vaccination. Vaccines, she thinks, are pushed by pharmaceutical companies to make money. “I know vaccines are designed to protect children from infection, but they are pharmaceutical products made by the same companies that make opioids,” she told me in a phone call.

In response to the proposed legislation, Pajer circulated an email to legislators, the Department of Health, and media outlets about what she considers to be the dangers of vaccines and how the media has erroneously reported on this latest outbreak of measles.

“These measles cases, most of which have now fully recovered, are being used to frighten the public into thinking they and their children are in grave danger from being publicly exposed to an infection that for the vast majority of Americans is benign,” the letter reads. As evidence, she cites Physicians for Informed Consent, an advocacy organization that Kathy Hennessey, the parent of a child on the autism spectrum and the head of Vaccinate Washington, says has “deep ties to pseudoscience.”

“Their take on measles being benign is troubling,” Hennessey says. And medical experts back this up: While it is true that most people who contract measles will have no complications, according to the Centers for Disease Control and Prevention (CDC), one in 20 children who contract measles will get serious complications like pneumonia, and one in 1,000 children will develop encephalitis, a swelling of the brain that can lead to permanent brain damage. Two in 1,000 children who contract measles will die from it.

Pajer, however, doesn’t trust the CDC. In her letter, she cites “CDC whistleblower” William Thompson, a scientist who was featured in the slickly produced 2016 movie Vaxxed: From Cover-Up to Catastrophe. The film shows happy, healthy kids who, according to their parents, became sick or disabled after receiving vaccines—sometimes overnight.

During the making of the movie, the alleged whistleblower didn't realize he was blowing the whistle. Rather, Thompson was unknowingly recorded by anti-vax advocate Bryan Hooker while discussing data omitted in a 2004 CDC study about vaccines and autism. It seems like a smoking gun, but Thompson himself has disavowed the film and its conclusions.

“I want to be absolutely clear that I believe vaccines have saved and continue to save countless lives,” he stated. “I would never suggest that any parent avoid vaccinating children of any race. Vaccines prevent serious diseases, and the risks associated with their administration are vastly outweighed by their individual and societal benefits.”

Still, anti-vax advocates routinely cite Thompson as evidence of some kind of CDC conspiracy. Pajer also argues that some children are “susceptible to vaccine injury.” This, she told me, "is well-established as fact."

Not, however, according to Douglas Diekema, a professor of pediatrics and bioethics at the University of Washington School of Medicine and a physician in the emergency department at Seattle Children’s. “We know that if you’ve had an allergic reaction to the first vaccine, you shouldn’t get the second,” he told me. But, still, there is no credible evidence an allergic reaction to any vaccine causes autism, despite hundreds of studies looking for a connection. The one blockbuster paper alleging a causal relationship, by Andrew Wakefield, was so riddled with methodological errors that it was later retracted, and no one has been able to replicate it.

“Researchers from multiple countries have published studies containing tens of thousands, if not hundreds of thousands, of children, and there is nothing there,” Diekema says. “And these are not people paid by drug companies. As a pediatrician, I take great offense to the idea that my colleagues and I would be in on this conspiracy.”

Diekema sees vaccine skeptics frequently in his work at Seattle Children’s. Parents will bring in a child with a dirty cut and are afraid that the tetanus shot will lead to autism or other "vaccine injuries." When this happens, Diekema describes what tetanus—an as-yet incurable disease that can result in death—could do to their children. This, he says, is usually—but not always—an effective way of communicating with parents. And research backs this up: According to a 2015 study, simply telling people what the experts say about contagious diseases rarely changes their minds. But if you describe what the disease does and show them photos of kids with measles, people are more likely to be moved.

The reality is, while we do know that vaccines don't cause autism, we don't know exactly what does. Diekema says there is some evidence that there’s a genetic component, but the research isn’t definitive. We don’t even know if the rate of autism has gone up. It’s possible there are more children on the autism spectrum than there were in previous decades ago, as many vaccine skeptics have claimed, but it’s also possible that doctors are just better at diagnosing it.

As for the Legislature's proposal to end all vaccine exemptions, Diekema says he has mixed feelings. When it comes to measles, he says, yes, no question. The disease is so highly contagious that all personal exemptions should end. But, he adds, ending the personal exemption also has the potential to create a backlash.

“I worry that if you eliminate that exemption for parents who are strongly opposed, you could inflame the community, and then you can find yourself in an even worse position,” he says. “But we should at least make it more difficult to get those exemptions.” Currently, all it takes to get an exemption is one visit to a physician, who will inform you of the risks and give you a note. Diekema thinks this should be an annual requirement instead. “It shouldn’t be easier to opt out of vaccines than it is to get vaccinated.”

If the Legislature does pass this bill, vaccination rates will likely go up, as they have in California since the state ended personal exemptions. That, however, is unlikely to convince Bernadette Pajer or her allies. As we've seen over and over, from battles over climate change to GMOs to vaccines, data is rarely, if ever, enough to sway people whose minds are already made up.