Guess which states are best at requiring vaccines? Not the ones you might think.

Seated in an ornate, columned hearing room before a panel of state legislators, the 7-year-old girl spoke with conviction.

“I love God with my whole heart,” she said. “He made our immune systems perfect.”

Therefore she — and other children from families with such religious beliefs — should be exempt from requirements to get vaccinated against measles and other infectious diseases, the girl argued.

A crowd of supporters erupted in applause. And within days, lawmakers tabled their effort to tighten the state’s school vaccination rules, leaving intact the option of obtaining a religious exemption.

A scene from a red state, perhaps? Somewhere in the Great Plains or the Deep South?

Try New Jersey, which has voted for Democrats in the last eight presidential elections.

The state’s vaccine impasse unfolded more than a year-and-a-half ago, just as the world was learning about a new infectious disease, yet to be named COVID-19. But as employers and hospitals grapple with the Biden administration’s new mandate to vaccinate or test adults for the coronavirus in large workplaces, public-health experts say valuable lessons can be drawn from what has worked at the school level.

» READ MORE: Medical exemptions for COVID-19 vaccines, explained

The term mandate may sound clear-cut, with no wiggle room. But the success of such policies can vary widely depending on how they are implemented, said Alison Buttenheim, an associate professor at the University of Pennsylvania School of Nursing, who studies the behavioral aspects preventing infectious diseases. And as the showdown in New Jersey illustrated, the vaccine issue transcends party lines.

The state’s Democratic lawmakers generally supported the move to eliminate religious exemptions and Republicans opposed it, but there were exceptions. And each year, New Jersey and many other blue states fall well short of getting every schoolchild vaccinated (think of left-leaning folks who espouse “natural living,” Buttenheim said).

Yet for decades, among the best states at school vaccinations are two in rock-solid red territory: West Virginia and Mississippi.

“Parents who don’t want to vaccinate their children,” she said, “come from every part of the political spectrum.”

West Virginia and Mississippi have two of the lowest rates of vaccination against COVID-19, and lately they have paid the price with jammed hospitals and school closures. Just 40% of West Virginians and 41% of Mississippians are fully vaccinated, according to Covid Act Now, a nonprofit that tracks pandemic trends.

But the states’ longtime success in school vaccination is built on firm policy, Buttenheim said: For decades, they were the only two states not to allow religious or personal-belief exemptions.

Opponents of the two states’ policies have attempted to chip away at them in recent years, proposing changes such as allowing religious exemptions for students in parochial and private schools.

But each year, pediatricians and other health providers come forward to testify against such proposals, successfully staving them off by citing the vast body of evidence that vaccines protect children, said Christopher Plein, a professor of public administration at West Virginia University who studies health policy.

A driving factor may be pragmatism, not politics, he said. West Virginia has a high poverty rate, and the benefits of a robust public health safety net are well-established. In 2014, for example, the state opted to expand access to Medicaid as allowed by the Affordable Care Act, unlike many conservative states.

Support for school vaccination stems from the same mindset, Plein said.

“It’s essentially baked into the West Virginia system,” he said.

California, New York, and Maine recently made similar efforts to get rid of exemptions for religious or philosophical reasons, but for the latter two, the change is too new to measure the impact (Maine’s took effect just this month). In California, improvement has been uneven, as lawmakers tweaked the policy over several years.

The state’s initial effort, which took effect in 2014, sought to limit exemptions based on personal belief by requiring parents to get a signature from a health-care provider — attesting that the parents were informed about the overwhelming benefits (and very slight risks) of immunization. Religious exemptions required no signature.

Vaccine rates rose slightly. Then came the measles outbreak of 2015, first identified in children who had been to Disneyland, and lawmakers clamped down further — eliminating all nonmedical exemptions, whether for religious or personal reasons.

California’s vaccination rates rose still more, but progress was bumpy. The number of medical exemptions tripled — the majority written by a small number of providers, in some cases selling the signed forms with no examination. More tweaks followed. Lawmakers added a list of conditions for which medical exemptions were allowed, and regulators now investigate when one provider signs an unusually high number of exemption requests.

“In California,” Buttenheim said, “they sort of got there in fits and starts.”

School vaccination rates have improved since the latest tweaks, hitting 96.5% with the combination MMR shot that includes measles. That is above the 95% threshold thought to be needed for herd immunity, but measles is very contagious. Areas of the state with lower vaccination rates could still drive outbreaks. And California remains outside the nation’s top 10. A small but growing number of families have avoided vaccine requirements by homeschooling their children or opting for a hybrid program called a charter home school, according to an analysis by Politico.

How these lessons will apply to adult vaccination against COVID-19 is unclear. In states that allow religious exemptions to school vaccination, including Pennsylvania and New Jersey, employers are expected to make the same allowance for adults and the COVID vaccines.

But policies can be designed to make such exemptions harder to obtain — what Buttenheim refers to as friction. Under the first set of California school-vaccine rules, for example, some who sought a personal-belief exemption likely were deterred by the requirement to get a doctor’s signature.

At Penn Medicine, employees seeking a religious exemption to the health system’s COVID vaccine requirement encounter plenty of friction. Rather than simply check a box, they must fill out a seven-page form with 12 detailed questions.

Among them: Employees must spell out whether they’ve sought exemptions to the health system’s flu vaccine requirement in previous years. If not, they must explain how their religious belief would preclude vaccination for COVID but not for the flu.

Some may find such demands burdensome. But according to a list compiled by Vanderbilt University Medical Center, the number seeking such exemptions should be very small. No major religions prohibit their followers from getting vaccines.

Friction also can be applied for those seeking medical exemptions. In West Virginia, for example, such requests must be submitted by a licensed physician and then reviewed by the state’s immunization officer, said Lisa M. Costello, an assistant professor of pediatrics at West Virginia University School of Medicine.

There is no question medical exemptions are necessary for a small number of people, said Costello, president of the state chapter of the American Academy of Pediatrics. Some may be allergic to an ingredient in a vaccine, for example. All the more reason to make sure they are granted only to those who really need them.

“By protecting everyone else who is able to be vaccinated,” she said, “we protect those who are not able to be vaccinated.”

She is among those who speak out against efforts to weaken the state’s vaccine rules, and so far she has been successful.

“I don’t think vaccination should be a partisan issue,” she said. “We have science.”

As the pandemic drags on, some wish the science on COVID-19 vaccines for kids would move faster. Just one (made by Pfizer and BioNTech) is authorized for emergency use in ages 12 and up. Until the FDA grants full approval for that age group, few school districts are expected to require the shots, though Los Angeles did so this month. Studies also are underway in younger children, and authorization for them could come by year’s end.

Science did not carry the day in New Jersey in January 2020, when state senators scrapped their effort to eliminate religious exemptions after the testimony from the 7-year-old girl, Emelia Walls of Cape May.

New Jersey lawmakers have reintroduced their proposal to ban religious exemptions. Democrat Herb Conaway, the bill’s sponsor in the state Assembly, where it passed in December 2019 before stalling in the state Senate, did not respond to a request for comment.

But in a floor speech to colleagues back then, Conaway, a physician, made his views clear, railing against “junk science.”

“It’s tragic that a child would die or suffer a grievous illness by a disease which is preventable by a vaccine,” he said. “Vaccines have been proven time and time again. Vaccine mandates have been proven time and time again to save lives.”