SACRAMENTO, Calif. -- A hotly contested California bill to impose one of the strictest vaccination laws in the nation would boost immunization rates by changing parents' behavior, according to immunologists and people who have researched the impact of such requirements.
Despite impassioned, ongoing pleas at the Capitol from parents seeking to maintain medical choice, a large portion of those who obtain personal belief exemptions are not fundamentally opposed to vaccination, said Dr. Mark Schleiss, a pediatrician specializing in infectious disease at the University of Minnesota.
Schleiss said most parents of unvaccinated children want to learn more and better understand the issues. Some parents, he said, simply find it more convenient to sign the back of a form or only partially vaccinate their children.
"I don't see the majority of parents being so committed to withholding vaccinations that their minds wouldn't be changed," he said. "I think this will have an impact."
The bill, sponsored by Democratic Sens. Richard Pan of Sacramento and Ben Allen of Santa Monica, would only allow children with serious health problems to opt out of school-mandated vaccinations. School-age children who remain unvaccinated would need to be homeschooled.
Hundreds rallied in opposition Tuesday ahead of an Assembly committee hearing on the legislation. The bill's critics have focused on potential risks associated with vaccines, saying shots could be tainted or otherwise dangerous. They've also characterized the proposal as government overreach and said supporters are exaggerating their case.
"You haven't had someone die from measles in the United States in 10 years," said Monica Sokoloski, a spokeswoman for advocacy group Our Kids, Our Choice. "That's proof the voluntary system is working."
If the legislation passes, California will join Mississippi and West Virginia on enforcing the strictest vaccine laws in the nation.
Dr. John Swartzberg, a clinical professor specializing in immunology at University of California, Berkeley, said eliminating the personal belief exemption is a silver bullet for California as it looks to strengthen its defenses against the spread of communicable disease following a December outbreak of measles at Disneyland that infected over 100 people in the U.S. and Mexico.
Data from the California Department of Public Health shows that the number of personal belief exemptions for incoming kindergarteners had been rising every year between 2010 until 2014.
But the tide turned in 2014 after the state overhauled its vaccine requirement. That stopgap measure, which required parents to obtain a signed waiver from their child's physician before claiming a personal belief exemption, proved just inconvenient enough to sway those who were "vaccine hesitant," Swartzberg said.
The percentage of personal belief exemptions claimed fell by 19 percent, settling at about 2.5 percent overall.
"That was the first evidence that using laws to impact behavior would actually be effective," Swartzberg said.
If SB277 passes, researchers believe it would provide another round of change for the state to reach what immunologists call "herd immunity," or the percentage at which enough people are vaccinated to protect the community as a whole.
The California Department of Public Health, however, has been hesitant to draw any conclusions from the slight 2014 increase in the immunization rate.
According to the Centers for Disease Control and Prevention, herd immunity for measles is between 92 and 94 percent. In 2014, 92.6 percent of California kindergarteners received the measles vaccine, but a number of suburban pockets outside major cities have vaccination rates far lower.
Dr. Rahul Gupta, West Virginia's state health officer, said allowing only medical exemptions has given West Virginia one of the highest immunization rates in the country.
The laws for schoolchildren have worked so well that West Virginia recently enacted a bill extending the policy, requiring children without a medical exemption be fully vaccinated before entering daycare as well.
The California bill would apply to elementary schools, secondary schools and daycare centers.
Opposition to the measure has been especially passionate online and in a series of rallies outside the Statehouse.