America defeated measles in 2000. Vaccine opposition brought it roaring back.

This is Part 1 of The Vaccine Divide, an updated data investigation into America potentially losing its measles-free status as the deadly virus roars back and childhood vaccine defenses continue to crack and crumble.

When Dr. Jeffrey Koplan took over as head of the Centers for Disease Control and Prevention in 1998, he and his colleagues pledged to stop the spread of measles in the United States within four years. They did it in two.

“We had a great vaccine,” said Koplan, now vice president for global health at Emory University. “Everyone was on board.” He attributed the success to widespread, bipartisan support from national public health groups, including the CDC and the Food and Drug Administration, as well as pediatricians and state health departments.

The virus receded, with only about 100 confirmed cases in the entire country that year. By 2000, a scourge of childhood was officially eliminated in the U.S.

Now, it has roared back. There have been 43 new outbreaks this year, with more than 5,000 confirmed cases, according to the CDC. Eight people, including four babies too young to be vaccinated, have died.

More than a year after an NBC News/Stanford University data investigation first revealed an alarming drop in childhood vaccination rates, an updated analysis finds cracks in the nation’s once-robust measles defense have widened into a chasm, particularly in the country’s most vulnerable areas.

Three-quarters of U.S. counties with recent data on kindergarten immunization rates are now below the recommended threshold for community measles protection, with more than half of counties dropping from the 2024-25 to 2025-26 school years.

This week, an independent commission of the Pan American Health Organization, a group within the World Health Organization, is meeting in Washington to consider whether the U.S. has lost its measles elimination status. The group of eight includes epidemiologists, infectious disease and vaccine experts from countries in the Americas, including the U.S.

After PAHO officials make a final decision, they will inform the U.S. Department of Health and Human Services, possibly this week.

Public health experts expect the group to revoke America’s measles-free status.

How the U.S. let its guard down

The country’s immunity was eroded by decades of scientifically dubious claims about the dangers of childhood vaccines. Misinformation then exploded during the pandemic, when shutdowns also led to interruptions in routine shots.

Thousands of Americans — nearly all unvaccinated — have been infected with measles in the last year and a half. Pregnant women are losing their babies. Doctors are scrambling to figure out how to treat the disease in newborns. Children are experiencing severe and sometimes irreversible neurologic complications.

“If we don’t get this under control, these numbers will only increase,” said Mark Jit, chair of the Department of Global and Environmental Health at the NYU School of Global Public Health. “Every year, the situation is just going to get worse.”

“We’ve forgotten how bad measles was,” said Dr. Georges Benjamin, executive director of the American Public Health Association. “In our forgetfulness, we’ve let our guard down.”

Since early 2025, public health workers have been in a whack-a-mole battle against measles, with epidemics in West Texas, Utah, Arizona, South Carolina and now Pennsylvania, Indiana, Ohio, Minnesota, New York and Wisconsin.

According to the new data, the fall of immunization rates in the least-vaccinated counties appears to be accelerating. During the 2024-25 school year, the top vaccination rate in those communities was 81.8%. Last school year, it fell to 79.2%.

An immunization rate of 95% is needed to prevent the spread of measles.

“The fact that this divide is getting greater is really worrisome,” said Dr. Richard Besser, a pediatrician and president of the Robert Wood Johnson Foundation, a nonprofit philanthropic organization focused on health research and programs. “What it should do is lead to public health action and engage trusted voices in vulnerable communities to recognize that vaccines aren’t about politics. They’re about protecting health.” Besser was acting CDC director under President Barack Obama.

Coverage in counties with the highest vaccination rates also declined, but much less so — from 99.3% in 2019 to 97.7% during the 2025-26 school year.

In a statement, the Department of Health and Human Services said that Secretary Robert F. Kennedy Jr and CDC director Erica Schwartz “continue to recommend MMR vaccination as the most effective way to prevent measles.”

If the Pan American Health Organization “removes U.S. elimination status, HHS and CDC will address the findings and work with partners to document interruption of endemic transmission and meet the requirements for re-achieving elimination status,” the statement read.

Small declines can have major implications

Measles is the most contagious virus in the world. It can linger in the air for hours after an infected person walks through a room. Nearly everyone who’s not vaccinated and is exposed to the virus will become infected.

The new data was culled from a wide variety of state and local documents, including some materials obtained under the Freedom of Information Act, and then condensed into the most comprehensive analysis of vaccinations and school exemptions to date.

Nationwide, 75% of counties and jurisdictions with measles-mumps-rubella vaccine data fall below the threshold needed for herd immunity for measles, a notable increase compared with 2024-25. And since 2019, vaccination exemptions have increased in the vast majority of counties — 86%.

Payne County, Oklahoma, experienced one of the most significant declines, from 95.6% in 2019 to just 78.4%. Vaccination rates in Scott County, Minnesota, which is outside Minneapolis, sank to 83% from 94.6% in 2019.

Some areas boosted vaccination rates. Washington, D.C., rose to 94.4% in 2025, from 78.5% in 2019.

Anti-vaccine attitudes take hold in Pennsylvania

The dangerous slide in vaccinations is playing out in real time in Pennsylvania, especially among the close-knit Amish community.

In hard-hit Lancaster County, the share of kindergartners who got MMR vaccinations in 2025-26 was 87.6%, NBC News data found. Before the pandemic in 2017-18, the county’s immunization rate was 95.5%.

That decline precipitated a deadly outbreak of measles this year that has spread mostly among Amish families in the state.

Ben Riehl, an Amish man living in Lancaster County, said he has witnessed fast-changing attitudes about vaccines over the past decade.

“Back in our day, you got the vaccine. There was no question,” said Riehl, 61. “It was the proper thing to do.” He and his wife vaccinated all six of their sons, who are now grown. Though Amish tend to resist mainstream medical interventions, there is nothing in the Amish culture or religion that is inherently anti-vaccine.

Riehl said that over time, Amish people couldn’t help but be influenced by anti-vaccine rhetoric, particularly when the message was brought directly to his community.

Before Kennedy, a longtime vaccine critic, became the nation’s health secretary, he was a keynote speaker at a 2021 event in Lancaster County, during which he said, without citing scientific evidence, that vaccines are harmful. The event drew more than 1,000 people — mostly Amish.

“The anti-vax crowd got the Amish people’s ear,” Riehl said. “The Amish didn’t suck the anti-vax ideas out of their own thumb. They were influenced by outside information.”

Dr. Evan Shirey, a pediatric infectious disease physician at Penn State Health Golisano Children’s Hospital in Hershey, said parents increasingly come into his clinic with worries about vaccines.

“We know that very prominently, individuals have come to our community specifically to spread the message that this virus isn’t a big deal,” said Shirey, who has been treating children sick with measles. “When we see that people are dying, when we see that babies are suffering, when we see that children are having illnesses that, in some cases, are permanent, we know that that’s a big lie. It’s just false.”

The onslaught of cases in Pennsylvania has caught some doctors off guard.

Lauren Shoup, 36, of Imperial, a Pittsburgh suburb, said she repeatedly questioned doctors about what to do after her 2-month-old daughter, Kieran, was exposed to measles during a routine visit with an allergist at the University of Pittsburgh Medical Center Children’s Hospital in early September. Because the first measles shot isn’t given until age 1, Kieran’s tiny body was defenseless against the virus.

Shoup said that when she took the baby in for a dose of antibody-rich immunoglobulin, which can be given within a short period of time after a measles exposure, she wasn’t given any directives about what her family could do to minimize risks to the community.

Three days after the baby received the antibody injection, Shoup said, an Allegheny County health department worker called her and said the infant should have been in quarantine since her exposure.

“I believe in science. I follow the science,” Shoup said. “But because no one knows the science, it’s very frustrating.”

In a statement, a UPMC spokesperson said the hospital system is “reviewing the concerns that have been raised and remain committed to working with public health officials and providing appropriate guidance to anyone who may have been exposed.”

In Allegheny County, which includes Pittsburgh, the measles vaccination rate dropped from 97.1% in 2019 to 92.9% last school year.

While babies are born with some protection if their mothers were vaccinated, it’s unclear how long that lasts. Kieran is now 4 months old, still too young for the MMR shots.

“It’s scary because she’s still not vaccinated,” Shoup said. “She’s still susceptible.”

Is measles already endemic in the U.S. again?

PAHO officials are looking at whether a single chain of measles transmission has gone on for more than 12 months, as well as whether there are a significant number of cases for which the source of infection is unknown.

In Utah, where measles flared up in June 2025, health officials haven’t yet declared an end to the outbreak. One case was diagnosed in the state recently, and the virus is still detected in wastewater samples.

Measles can spread so quickly that even one case is considered an outbreak.

Through the 1990s, the CDC and the FDA worked together with “a sense of common purpose,” along with federal and state leaders and pediatricians, to encourage MMR vaccinations, said Koplan, who was appointed head of the CDC by President Bill Clinton and continued in the role when President George W. Bush took office.

“Science is now ignored, and people die from ignoring science,” Koplan said.

If the U.S. loses its measles elimination status, it will join Canada — the only other country in the Americas that has lost control of the virus — paving the way for more illnesses and deaths.

“We’re going to have to stop the runaway train, and then we’ll need to turn it around and start going in the other direction,” Noel Brewer, the chair of an independent committee that assists the CDC in analyzing the country’s measles situation, said ahead of the PAHO meeting.

Before the MMR vaccine, about 500 people died from measles complications every year, most of them children.

That’s nearly half the number of kids who die annually in the U.S. from cancer.

“Measles has not disappeared because it’s harmless,” Koplan said. “It’s disappeared because vaccination programs have been effective.”

Aria Bendix contributed.