A small but growing measles outbreak in central Ohio has sickened at least 77 children, almost all under age 5. The vast majority are either unvaccinated or have received just one of the two recommended doses of measles, mumps and rubella vaccine, according to City of Columbus Public Health.

More than a third of the children have been hospitalized.

The outbreak, the largest in the U.S. since 2019, is happening as resistance to school vaccination requirements is spreading across the country.

On Friday, the Kaiser Family Foundation released data showing that 28% of adults surveyed this summer were against vaccination requirements for kids entering kindergarten, up from 16% in 2019.

The percentage of parents who said they were against vaccination requirements for school was even higher. This year, 35% of surveyed parents said it should be up to moms and dads whether to have their kids vaccinated, up from 23% in 2019.

“That’s a pretty substantial change in three years,” said Lunna Lopes, a senior survey analyst for KFF’s Public Opinion and Survey Research team.

The main driver of the increase has been the debate over vaccination mandates during the pandemic, Lopes said. The survey did not suggest people stopped believing in the need for vaccines; rather, the change reflected a shift in attitudes toward vaccination requirements to attend school.

“It was the controversies and the climate of Covid vaccines and the vaccine mandates that had an impact,” Lopes said.

Tens of thousands of children across the U.S. have already fallen behind in vaccinations for diseases like measles, chickenpox or polio, a trend that has been bubbling for years but accelerated during the pandemic.

Doctors’ appointments missed during the first years of Covid contributed to a dip in childhood vaccination rates, but it’s the onslaught of vaccine disinformation that continues to put young kids at risk for preventable death and disease, Dr. Rochelle Walensky, the director of the Centers of Disease Control and Prevention, told NBC News.

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“As I think about the challenges that we have to public health, vaccine misinformation is among the biggest threats,” she said.

The CDC is expected to release new data on the rate of childhood vaccinations early next year. In its last report, the number of fully vaccinated kids entering kindergarten in the fall of 2020 fell by 1% compared to the previous year.

It’s not just routine vaccinations that have taken a hit.

Just 42% of kids under age 18 have had their flu shots this year, according to CDC data. And the American Academy of Pediatrics said the vast majority of kids ages 4 and younger — 90% — have not gotten the updated Covid shot.

The dip in vaccinations has called attention to communities that remain susceptible to otherwise rare illnesses. While the national decrease of 1% seems small, the declines have been more significant in some states. Childhood vaccinations dropped by 13% in Washington. In Alabama, some vaccinations were cut by more than half compared to pre-pandemic rates.

There needs to be very high level of immunity in the population to keep highly contagious diseases like measles at bay, said Dr. Buddy Creech, a pediatrician and the director of Vanderbilt University Medical Center’s Vaccine Research Program in Nashville, Tennessee.

“The best example of that is measles,” Creech said.

The vaccine to prevent measles, given once around age 1 and then again at age 5, is extraordinarily effective, preventing 97% of cases. Because of widespread vaccination efforts, the virus was considered eliminated in the U.S. in 2000.

Walensky worries that people no longer feel measles, which killed around 128,000 people globally in 2021, is a real threat.

“We have suffered the consequences of our own successes,” she said.

The CDC has sent teams to Ohio and other under-vaccinated areas of the country that have experienced vaccine-preventable illness.

“Here in Ohio, we have some pretty active anti-vaccine groups,” said Tara Smith, a professor of epidemiology at the Kent State University College of Public Health. “I’m really worried that this is something that is becoming more entrenched here.”

Walensky said that once a parent becomes frightened by false or inaccurate claims about vaccine risks, it is difficult to ease that fear, even with facts.

“As moms, we know that the biggest force is to try and protect your children,” she said.

One of the biggest hurdles is getting through to parents who, based on rumor or false information, truly believe vaccines cause harm.

“It’s not because they want to harm to their child or they don’t care enough to seek out the best information,” Creech said. “It’s that they’ve received information, sometimes from what seems like a credible source, that’s just not true.”

Who is the ‘trusted voice’?

Even as pediatricians like Creech and public health officials try to navigate a “whack-a-mole” strategy of fighting anti-vaccine rumors and twisted facts, the CDC has no plans to create a department within the agency with the sole purpose of addressing vaccine misinformation head-on, Walensky said.

Walensky, an infectious disease doctor with more than two decades of experience, concedes that she, as the CDC’s director, may not be the best person to communicate about vaccine safety.

“I may not be the trusted voice,” she said. “Messaging at a national level is not going to necessarily reach the communities that are under- and unvaccinated.”

The best way to break through vaccine misinformation (false or inaccurate information) and disinformation (which occurs when people spread rumors or hoaxes about vaccines to create fear) is to use trusted people already entrenched in communities, including local health leaders, pediatricians, even pastors, Smith said.

“There is not any kind of one-size-fits-all messaging that’s going to do this,” she said. “We need all hands on deck.”

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This article was originally published on NBCNews.com