Ellen Siegel wasn’t sick when her flight from Stockholm touched down in New York City on a late July day in 1963. Her skin was free of rashes and redness, her temperature normal.

But the 69-year-old American was missing the one thing she needed to convince medical inspectors at Idlewild Airport that she didn’t pose a threat to public health: valid vaccination papers.

A deadly smallpox outbreak had swept through the Swedish capital that summer, and health officials were screening international travelers by the thousands in hopes of stopping the grisly virus from crossing the Atlantic. “We should not play Russian roulette with the health of this country,” one wary inspector said at the time.

When Siegel couldn’t prove she was vaccinated, authorities ordered her quarantined in a government hospital, prompting a legal challenge by Siegel’s family that still stands as the only federal court battle over the government’s quarantine powers in more than half a century.

The current coronavirus epidemic marks the first time since Siegel’s case that the federal government has ordered people involuntarily quarantined to stave off a potential public health crisis — and its authority to do so remains vast and virtually uncheckable in most cases, just as it was it was six decades ago.

Under an emergency declaration from the Trump administration, hundreds of evacuees from the coronavirus hot zone in China’s Hubei province have undergone mandatory 14-day quarantines on military bases around the country. Others who were exposed to the virus aboard the ill-fated Diamond Princess cruise ship are in the middle of their own two-week quarantine, biding their time under the watchful eye of government physicians until the disease incubation period passes.

The actions to prevent a coronavirus outbreak on U.S. soil underscore the federal government’s outsize power to detain people in the name of public health, even if they pale in comparison to China’s decision to put tens of millions of people around the disease epicenter on lockdown.

Regulations set forth by the Centers for Disease Control and Prevention give health officials broad authority to quarantine or isolate anyone “reasonably believed” to have been exposed to a range of maladies, including cholera, infectious tuberculosis and flus that can cause a pandemic.

This exceptional power is rooted in the Constitution’s Commerce Clause, which allows Congress to regulate foreign and interstate business. Quarantine involves the temporary confinement of people who may have been exposed to a disease but haven’t developed symptoms; isolation separates people who are infected with a disease until they are no longer contagious. The federal government is free to use either when the circumstances call for it.

“It’s like a curfew or an evacuation order if a natural disaster occurs. Just like when a hurricane is bearing down, people are ordered to leave coastal areas because no one can save them,” said Scott Burris, director of the Center for Public Health Law Research at Temple University. “If we have a reasonable prospect of stopping or slowing this virus, even if we’re doing it with mittens on, the government can take emergency action.”

The federal government seldom exercises this authority, but that’s mostly because it doesn’t have to. State and local governments generally take the lead in quarantine decisions, bearing the primary responsibility for the health of their residents. When disease outbreaks do occur, health officials often opt for voluntary quarantine or isolation rather than try to compel it. People tend to follow the instructions.

Authorities weren’t taking any chances in 1963. That May, a 24-year-old Swedish seaman contracted smallpox during a trip through Southeast Asia and carried the disease back home to Stockholm. In the weeks that followed, the virus spread to two dozen more people, killing four of them.

The outbreak triggered a global health scare that summer. At Idlewild Airport, inspectors screened more than half a million passengers over a three-month period, eyeing them for symptoms and scrutinizing their paperwork, as the New York Times reported at the time.

One of those passengers was Ellen Siegel, who had spent four days in Stockholm before flying to New York on July 25 to visit her daughter. She insisted that she had been vaccinated weeks prior, but health officials concluded that her latest injection and others before that had been “unsuccessful,” court documents show. They ordered her quarantined for two weeks at the U.S. Public Health Hospital in Staten Island.

Siegel’s daughter, an attorney, immediately tried to get her mother discharged by filing a habeas corpus petition, a legal tool typically used to free criminal defendants from jail. She argued there was no evidence that Siegel was exposed to smallpox and noted that the outbreak had tapered off weeks before Siegel arrived in Stockholm.

U.S. District Judge John F. Dooling rejected the petition and ordered Siegel to remain quarantined for the full 14 days.

“The judgment required is that of a public health officer and not of a lawyer used to insist on positive evidence to support action,” Dooling wrote. “Their task is to measure risk to the public and to seek for what can reassure and, not finding it, to proceed reasonably to make the public health secure. They deal in a terrible context and the consequences of mistaken indulgence can be irretrievably tragic.”

Health officials, the judge continued, “were not free and certainly not bound to ignore the facts that opportunity for exposure existed during four days in Stockholm, that no one on earth could know for fourteen days whether or not there had been exposure, and that Relator, with a history of unsuccessful vaccinations, was peculiarly in a position to have become infected and to infect others.”

The circumstances surrounding Siegel’s case are far different in scope and impact from the coronavirus outbreak. The current epidemic has killed more than 2,400 people and sickened some 77,000. And there has been no sign that anyone wants to challenge the Trump administration’s quarantine orders in court, even as some legal experts and advocacy groups such as the American Civil Liberties Union warn of their potential to infringe on people’s due process rights.

If a court challenge did emerge — an unlikely scenario given that the CDC’s rules require an appeal through the agency first — judges would likely defer to public health officials, said Wendy K. Mariner, a health law professor at Boston University and author of a 2018 paper examining the intersection of civil rights and federal quarantine powers.

“They would be as concerned as anyone in the public about releasing a person who might have an infection,” Mariner said. “You want to be on the side of prevention.”

Moreover, she added, “People are pretty compliant as long as they believe that their best interests are being taken care of.”