(CNN) At a time when almost everything is politicized, vaccination has planted itself squarely on the national stage.

On one side of the debate are parents who are rebelling against settled science and calling on states to broaden vaccine exemptions. They cite their faith or believe vaccines pose danger to their children, even though no major religion opposes them and claims of vaccines' link to autism has been long debunked.

On the other, are public health officials who point to unprecedented measles outbreaks that have sickened thousands in the US as proof that vaccine exemptions cause health crises. They're calling on states to eliminate exemptions entirely.

With 2020 legislative sessions kicking off in most states this month, this push and pull between science and skepticism is playing out across the country. More and more lawmakers are proposing bills, seeking to either boost, or limit, mandatory vaccinations for schoolchildren.

"I won't be surprised if we see many pro-vaccine bills this year," said Dr. Sean O'Leary, a member of the American Academy of Pediatrics Committee on Infectious Diseases. "The measles outbreaks were really a wake-up call, showing legislators that maintaining high vaccination rates is not just a theoretical goal."

O'Leary said he won't be surprised if some antivaccine bills are introduced this year, "but I doubt any will pass."





Some want to ban religious exemptions, citing science



And last year, 14 states proposed eliminating religious exemptions for vaccines -- a marked increase from years past, according to the An overwhelming majority of American adults (88%) say the benefits of the measles, mumps and rubella (MMR) vaccine outweigh the risks, according to a new Pew Research Center survey And last year, 14 states proposed eliminating religious exemptions for vaccines -- a marked increase from years past, according to the American Academy of Pediatrics

New York, California and Washington state all voted to end some vaccine exemptions for children who attend public schools, and Maine enacted similar legislation, though it won't take effect until September 2021.

New Jersey was poised to join them this week, but lawmakers pushing a religious exemption law said they didn't have the votes. Thousands of anti-vaccine protesters swarmed the New Jersey statehouse, even though public health officials say the benefits of vaccines are not a matter of opinion.

"Science is really on the side of vaccinations," said O'Leary, who is an associate professor of pediatrics at the University of Colorado School of Medicine. "They're one of the best public health interventions in history in terms of the numbers of lives saved. The benefits far outweigh the risk."

A pro-vaccination supporter at a March for Science on April 14, 2018, in Portland, Oregon.

Others want to ban mandatory vaccinations, citing personal belief

While they are outnumbered, vaccine opponents are a vocal bunch, and they've caught the ears of state lawmakers.

Currently 45 states and Washington, DC, grant religious exemptions to vaccines, according to the National Conference on State Legislatures , which tracks state laws.

Barbara Loe Fisher is president and co-founder of the National Vaccine Information Center, a group that advocates for vaccine exemption. She sees the issue as a matter of personal freedom.

"We need to have the ability in our country, if we find a commercial pharmaceutical product is not as safe and effective as we're being told it is, we should have the right to make informed consent to use the product," she said.

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Where the truth lies

Support for vaccine exemptions persists despite bunk studies that have erroneously linked vaccines to autism and the near-universal agreement among government health agencies and healthcare professionals that vaccines are safe and effective.

The Centers for Disease Control and Prevention say there's a 1 in one million chance of having a serious reaction to a vaccine.

The American Academy of Pediatrics' official stance -- one it shares with most other medical organizations and agencies -- is that non-medical exemptions should be eliminated completely, O'Leary said. That includes religious and personal exemptions.

"When vaccination rates fall, we see disease, and people suffer. Protecting children in schools is a worthy goal of government, regardless of political affiliation," he said. "There's really no good reason to exempt your child from vaccination -- only medical."

Children who can't be vaccinated for medical reasons benefit from their vaccinated classmates, he said, but if fewer children are getting vaccinated diseases can spread more easily between them.

"When you choose not to vaccinate, you're putting your child at risk of disease, but you're also putting other people at risk," O'Leary said.

Measles outbreaks have forced states to react

New York, California and Washington state took action after massive measles outbreaks in 2019, a year that saw the highest reported measles cases since the disease was declared eliminated nationwide in 2000.

But lawmakers looking to abolish religious exemptions in Florida and Colorado last year were derailed by protesters.

Anti-vaccine protesters outside the state house in Trenton, New Jersey, on January 13, 2020.

The stricter a state's vaccination laws, the fewer nonmedical exemptions and fewer outbreaks of vaccine-preventable diseases. When those exemption laws are loosened, the reverse is true.

But bills that seek looser restrictions are "almost universally" killed in committee, O'Leary said.

Supporters of vaccine exemptions see laws like those passed in New York and Washington as "fundamentally a threat to their ability to make informed consent about vaccinations," said Fisher, president of the National Vaccine Information Center.

The organization supported 77 vaccine-related bills during the 2019 legislative session, the most since it began tracking state legislation in 2010. The bills didn't all pass, but they're evidence that "lawmakers are listening to constituents" about anti-vaccination measures, Fisher said.

The vaccine debate doesn't always fall along party lines

Proponents on both sides of the debate have found allies across the political spectrum. Republican lawmakers have sponsored stricter bills, and Democratic governors have drawn the line at mandating vaccines.

Washington state Rep. Paul Harris, a Republican, sponsored the state's vaccination bill after the district he represents saw 71 measles cases in 2019.

The Washington bill was unique: It specifically concerned the MMR vaccine and it wasn't limited to public school students. The state now requires almost every student, at public and private schools and daycare centers, to have the MMR vaccine.

The New Jersey Senate conducting business on January 13, 2020 -- the day lawmakers agreed to table a vote on legislation to eliminate most religious exemptions for vaccines.

"It's a tough balance, but you're using a public -- and private -- resource in conjunction with lots of other kids," Harris told CNN. "There are other venues where they can be educated, they can still have their freedom, but they're not going into a public school and spread their disease."

Concerned constituents have told him the law infringes on their personal freedom, he said.

"It's a very vocal minority," he said. "But they aren't being forced to be vaccinated -- they just can't come to schools."

Harris believes the science about vaccines is straightforward. He said the state wasn't aggressive enough in its response before the measles outbreaks occurred.