Last week, the Colorado Senate passed a bill that would make it more difficult for parents to opt out of vaccinating their children. On Monday, hundreds of demonstrators showed up in hopes of blocking the bill’s passage in the state House.

It’s a scene that has been replayed recently in capitals across the country. Last month, more than 500 people showed up to testify about a vaccine bill in Connecticut, stretching a committee hearing out to more than 21 hours. In January, New Jersey lawmakers pulled a bill that would have ended religious exemptions for vaccines after weeks of sustained protests against it.

On Tuesday, voters in Maine rejected, by an overwhelming margin, a measure that would have overturned a law passed last year to eliminate non-medical exemptions. Despite the defeat, vaccine skeptics are undaunted -- and well organized.

“The fact that enough people came out and got the signatures required to get it on the ballot, and that there are many legislators supporting this effort, shows that this is not a cut-and-dry issue,” Dawn Richardson, advocacy director for the National Vaccine Information Center, a nonprofit group opposed to universal vaccination requirements, said before Tuesday's vote. “There’s obvious division on it.”

For years, legislators sought to distance themselves from that division. Although the number of parents who are skeptical about vaccines has been growing for a couple of decades, most states have kept exemptions on the books. Recent outbreaks of preventable diseases, however, have prompted some lawmakers to make it harder for parents to opt out.

“There were enough people who were choosing to exempt themselves from vaccines, and diseases came back,” says Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

In Colorado, for example, 87.4 percent of kindergarteners have received the measles, mumps and rubella (MMR) vaccine — one of the lowest rates in the nation and well below the 95 percent rate sought by both the federal Centers for Disease Control and Prevention and the Senate-passed bill. Connecticut has seen a 25 percent year-over-year spike in religious exemptions. Non-medical exemptions have also been growing in Maine, leaving the state with the sixth highest rate of such exemptions during the last school year. All told, the percentage of unvaccinated children has increased fourfold since 2001.

“We unfortunately talk to people on a daily basis who have lost their children to vaccine-preventable diseases,” says Erica DeWald, advocacy director for Vaccinate Your Family, a pro-vaccine advocacy group. “A whole other group of parents are terrified their kids are going to school with unvaccinated kids.”

The Hunt for a New Vaccine

With the new coronavirus spreading across the country, most of the public would welcome the protection of a new vaccine. It’s possible that dynamic could shift the debate around the broader vaccination question.

“We could have lots of problems before a vaccine is available,” says Jack Pitney, a government professor at Claremont McKenna College who has written critically about vaccine exemptions. “That long, unhappy period could remind people about the value of vaccination.”

But DeWald notes there have been public health scares in the recent past that haven’t pulled off that trick, including anthrax and H1N1. DeWald and other vaccine supporters believe that the whole idea of inoculation has been a victim of its own success.

“When you hear celebrities like Jenny McCarthy say that, 'between the vaccine and measles, I’ll take measles every time,' it shows we’ve not only eliminated measles but the memory of measles,” Offit says.

Polls indicate that the vast majority of Americans support vaccines. According to a Gallup poll released in January, 84 percent believe that vaccinating children is important. That number has dropped, however, from 91 percent at the start of the century.

There are now a number of organized groups who are staunchly opposed to mandated vaccinations. They insist that they’re not opposed to vaccination, but contend that not all vaccines are equally safe and effective. They argue that parents should be able to make informed choices for their families.

“Who do you think cares most about their children — do you think it’s the parents or the drug producers?” says Mary Holland, general counsel for Children’s Health Defense, an anti-mandatory vaccine group chaired by Robert F. Kennedy Jr. “This is a voting issue for people on the right and the left. This is about their kids.”

Those who are skeptical or hesitant about vaccines may hold a minority viewpoint, but their staunch advocacy and sometimes aggressive tactics have made the vaccine issue a difficult one for legislators.

“You’re going to see this issue become more and more contentious in the states,” Richardson says.

There’s Always Been Pushback

The idea of universal vaccination has always met with resistance. In 1796, Edward Jenner developed the smallpox vaccine, which over the next quarter-century cut the death rate from the disease in half. In 1867, the British government passed a law making the smallpox vaccine compulsory under penalty of fines and possible imprisonment. “Compulsory vaccination spawned the first anti-vaccine movement,” Offit writes in his 2015 book Deadly Choices: How the Anti-Vaccine Movement Threatens Us All.

With the advent of the polio vaccine during the 1950s, there was in fact real and demonstrated harm. A small pharmaceutical company called Cutter Laboratories failed to fully deactivate the virus, leading to 70,000 mild cases of polio and 10 deaths. It was one of the worst biological disasters in U.S. history, Offit writes. Yet, he notes, demand for the vaccine from other manufacturers did not abate.

More recently, there was concern about thimerosal, a preservative that contained mercury and was used in some childhood vaccines. Studies showed thimerosal to be safe and not be linked to autism, but it has not been used in childhood vaccines since 2001 due to parental concerns.

Following measles outbreaks during the 1970s, states began to mandate vaccines for children attending public schools. Those laws faced pushback as well. In the end, all but two states — Mississippi and West Virginia — allowed for religious or philosophic exemptions.

In 1998, a study purported to show a link between the MMR vaccine and autism. That study was withdrawn in 2010 and has been refuted by numerous other studies, but it helped fuel skepticism and even downright hostility to vaccines — particularly the MMR vaccine.

“Each child is different and each vaccine is different,” Richardson says. “Some can be harmful for some people.”

Although billions of doses have been injected into millions of people since the National Vaccine Injury Compensation Program was created, only about 6,600 people have been compensated for harm they claim was caused by one of 16 vaccines. Harm was not proven in most of those cases. “Approximately 70 percent of all compensation awarded by the VICP comes as a result of a negotiated settlement between the parties in which HHS has not concluded, based upon review of the evidence, that the alleged vaccine(s) caused the alleged injury,” according to the Health Resources and Services Administration.

Failure to vaccinate can cause real problems. An anti-vaccine group in Minnesota highlighted the debunked MMR study among Somali Americans living in Minneapolis. Between 2004 and 2010, the MMR vaccine rate among Somali children in Minnesota dropped from 91 percent to 54 percent, according to the federal Centers for Disease Control and Prevention. During a 2017 measles outbreak in the Minneapolis-St. Paul area, 64 of the 79 confirmed cases were in Somalis, with 74 cases in unvaccinated or undervaccinated individuals.

Last year, there were almost 1,300 cases of measles in the U.S., the most since 1992.

“Get to a few thousand, and people would die,” Offit says. “The choice not to get a vaccine is not a no-risk choice. It creates different and more serious risks. This isn’t a choice they’re making just for themselves and their children. It’s a public health issue.”

A Slew of Bills

Legislatures are now weighing more than 200 vaccine-related bills, according to the National Vaccine Information Center. They are roughly divided in number between those that would make it harder to avoid vaccinations and those that would give parents greater leeway or provide them with more information.

Health groups such as the American Medical Association support limiting the ability to opt out of immunizations. Some states are considering joining the few that allow older or “mature” minors to consent to vaccination, even when their parents object.

Richardson says the fact that most states considering reducing or eliminating exemptions have rejected the bills shows that “this is not a popular position.”

She contends that the pharmaceutical companies are backing the anti-exemption bills to line their own pockets. Merck and Pfizer each contributed $250,000 to defeat the referendum in Maine. Drug companies spend millions annually on campaigns and lobbying — after losing credibility in some quarters, given the opioid epidemic and accusations of price gouging.

But anti-vaccination groups have also benefited from wealthy donors, including a hedge fund manager and a physician who has made millions selling natural health products.

No one doubts that thousands of parents are sincerely motivated by a desire to protect their children. “If you look at it from their perspective, these are parents who are made to believe their children are injured, so they’re very passionate,” says DeWald, of Vaccinate Your Family.

That passion can sometimes spill over into intimidation. Last summer, an anti-vaccine activist was cited for assault after shoving California state Sen. Richard Pan, the lead sponsor of the state’s anti-exemption law. In October, another protester spattered senators with a small amount of menstrual blood from the Senate’s visitor’s gallery. Colorado state Rep. Kyle Mullica, a sponsor of pro-vaccination legislation, received death threats last year, including a threat to burn down his house with his children in it.

Richardson says such incidents are purely the products of disturbed individuals and not supported by any organized group. Still, doctors such as Offit who are prominent pro-vaccine spokesmen have received enough serious death threats to receive police protection at times. And vaccine skeptics are known to be highly vocal on social media.

“They are generally the most aggressive, hostile, rudest and threatening group of people I have ever experienced as a legislator,” Bob Duff, majority leader of the Connecticut Senate, told the New Haven Register Citizen after needing a security escort to leave a forum on the issue last month.

Parents who advocate stronger vaccination mandates in the media and in statehouses can find the experience to be intimidating, says DeWald. “These people who have lost children can be heckled when they stand up and testify,” she says.

But DeWald and other mandate supporters recognize that they have to try to match the emotion and energy that vaccine skeptics bring to the debate. Making the case clinically is not the same as making it politically.

As opposition to mandatory vaccines continues to grow, countering that movement will require compelling storytelling, not just statistics.

“It’s disappointing to see so many politicians yield to the anti-vaccine people,” says Pitney, the Claremont McKenna political scientist. “They’re buying a few minutes’ peace and quiet by jeopardizing the long-term health of school children.”