Dr. Adam Ratner hovered over a gravely ill infant in a New York City intensive care unit on a grim day in 2022. The 3-month-old girl spiked a fever two days earlier and had become lethargic. Soon she was having seizures and struggling to breathe.

She didn’t register Ratner’s towering frame or the bright hospital lights. Her eyes stared up and to the right, eerily frozen.

He ran his hand over the soft spot on her head, which should have been flat. Instead, it bulged, a sign that too much fluid was building up inside her skull.

The baby’s life was in danger, and Ratner needed to figure out why. He worried the culprit was bacterial meningitis, an infection of the membranes that protect the brain.

What came back on her lab tests was something out of the history books.

The infant’s meningitis was caused by invasive Haemophilus influenzae type b, or Hib, a type of bacteria that used to kill nearly 1,000 children a year in the U.S. A shot introduced in the late 1980s was so effective that Ratner, a veteran pediatric infectious disease doctor, was among the generations of physicians who had never seen a case. But the baby’s parents, Ratner learned, had chosen not to vaccinate her.

Disheartened, he told his colleagues, “This should be a never event.”

It wasn’t. The following year, Ratner treated another infant with Hib, then another, each of them unvaccinated. Two went home, but one had to be discharged to a rehabilitation facility. That 5-month-old boy had huge black pupils that didn’t respond to light, and he needed a ventilator to breathe. Ratner and his colleagues noted an “absence of brain stem reflexes,” indicating severe damage.

The U.S. government took a half century to build a vaccination system that shielded children from such a fate. Its success depended on two fundamental pillars: parents trusting in vaccines and children having access to them. Both are now in peril, thanks in no small part to the man steering America’s health policy.

Health and Human Services Secretary Robert F. Kennedy Jr., who founded an antivaccine group and once likened the immunization of children to a holocaust, is transforming a government that long championed the lifesaving benefits of shots into one that spreads doubts about their safety here and abroad.

Kennedy is also considering changes that could prompt the few companies that make vaccines for American kids to abandon the U.S. market, leaving parents who want the shots unable to get them.

The threat to vaccine access reaches across the globe after Kennedy yanked the government’s $1.6 billion pledge to the aid group that provides shots for the world’s poorest children. For decades, the U.S. had funded such work not just as a humanitarian mission but as a way to keep Americans safe from unchecked contagions.

Kennedy’s efforts to reshape vaccine policies have been well chronicled, but ProPublica wanted to take a broader look at how the changes might affect Americans’ health in the years to come.

We found that long-forgotten plagues have roared back, killing and maiming children in parts of the world where access to vaccines or trust in them faltered. What seemed like subtle changes to a country’s vaccine policies had disastrous consequences years later.

Even in places that offer highly advanced health care, doctors have felt impotent trying to undo the damage when these horrors return. Modern medicine can’t reverse paralysis from polio. Surgeons can intervene when a baby is born blind, deaf and with heart defects after being exposed to rubella in the womb, but the child is still likely to face a life shaped by disability.

ProPublica reviewed hundreds of studies on vaccines and outbreaks of the diseases they prevent and interviewed more than three dozen people who have worked on U.S. immunization programs here and abroad, dating back to the days of smallpox. Some had never spoken publicly about their experiences.

They shared a pit-of-the-stomach dread that American children will end up fighting for their lives against infections that have long been preventable.

“I think there always was a worst-case scenario,” said Dr. Melinda Wharton, who retired last September after more than three decades leading immunization programs at the Centers for Disease Control and Prevention. “I don’t think I imagined it could or would be this bad.”

This week, Kennedy’s agency indicated it planned to appeal a federal court ruling that halted, at least temporarily, some of his changes. Among those was the decision to drop six diseases from the routine childhood immunization schedule.

HHS declined to make Kennedy available for an interview. In an emailed response to detailed questions, HHS spokesperson Andrew Nixon said that the agency has not limited access to or insurance coverage for vaccines. During the prior administration, federal health agencies “told the public that questioning vaccine policy was off limits,” Nixon said. “That posture contributed to a collapse in trust in U.S. health care.”

“Secretary Kennedy believes that trust is rebuilt through an open review of safety data, the willingness to ask the hard questions, and ensuring the American people have all emerging information as soon as we know it,” he said.

Vaccination rates have fallen in large swaths of the country. Resentful of how government institutions responded to the COVID-19 pandemic, many Americans lost trust in public health leaders. Antivaccine activists spread misinformation and recast the once-fringe practice of refusing shots as an exercise in “medical freedom.”

Now the U.S. is experiencing a surge in measles not seen in three decades. There have been more than 3,600 cases across 46 states and three deaths since January last year. The virus spread so fast in South Carolina this year that some medical teams had to examine infected patients in their cars to protect vulnerable people in their waiting rooms, like they did during the worst days of COVID-19.

Measles, among the most contagious diseases, is typically the first to infect undervaccinated communities and serves as a warning that other scourges will follow.

That’s what happened in New York City where antivaccine forces distributed illustrated handouts that seeded fear in Orthodox Jewish communities. Ratner saw a direct line between a loss of trust and the sick children in his ICU — first with measles in 2018 and 2019, then with Hib a few years later.

Now the villainization of vaccines isn’t coming from pamphlets passed out on a Brooklyn street corner. It’s coming from the highest health offices in the U.S. government.

“I’m worried,” Ratner said, “that we’re going back to a time where people die in childhood.”

The U.S. has been a leader on vaccination since the nation’s founding.

During the Revolutionary War, George Washington ordered troops to be inoculated against smallpox, which had ravaged the Continental Army and was scaring away recruits. Washington knew the perils of the disease: His face was pocked with scars from his own teenage infection.

The inoculation, the country’s first immunization mandate, took a primitive form. A sore from a smallpox patient was lanced, then the pus was inserted under a healthy person’s skin. Though some people died, the resulting infection was, for the vast majority, milder than the type caught in a bunkhouse or on a battlefield.

Washington gave the order in February 1777, “keeping the matter as secret as possible” so that the British wouldn’t attack his bedridden troops during their monthlong recovery. Had he not carried out the inoculation, many historians have concluded, the British may have won.

Nearly two centuries later, in the throes of the Cold War, CDC scientists teamed up with their counterparts from America’s archenemy, the Soviet Union, to wipe smallpox from the planet. They worked through the World Health Organization to track the virus in cities, rainforests and war zones, vaccinating those at risk. Four U.S. presidents, Democrats and Republicans, backed the work until the disease that had haunted humans since the days of the pharaohs was gone.

Vaccines, for decades, weren’t politically divisive. They were so uncontroversial that McDonald’s restaurants in the 1990s put the childhood immunization schedule on their tray liners.

When the nation’s immunization program was in trouble in the 1980s, Republicans and Democrats stepped in to save it.

Vaccine makers were abandoning the U.S. market after a flood of lawsuits alleged that the shot used at the time to protect children from diphtheria, tetanus and whooping cough caused profoundly disabling seizures. Scientists later discovered genetic causes of some of the most devastating forms of epilepsy, but parents who sued back then won big verdicts and settlements.

At one point pediatricians could only buy that shot from a single company, and there were shortages. The U.S. also was down to just one manufacturer for the measles-mumps-rubella shot and one for the polio vaccine.

“If there is a fire tomorrow in the plant where the polio vaccine is manufactured, what would happen?” Rep. Henry Waxman asked the CDC director during a 1984 House subcommittee hearing.

“We would have a shortage,” the director answered.

An exasperated Waxman shot back: “Are we going to then start putting money into iron lungs for polio victims?”

A liberal Democrat from California, Waxman for years worked with Sen. Paula Hawkins, a conservative Florida Republican, on legislation that stopped the exodus of vaccine makers by limiting their liability. Launched in 1988, the federal Vaccine Injury Compensation Program pays people who suffer rare but serious side effects, using money from a special tax on certain shots. The program maintains a table of injuries that........

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