After the Houston Methodist Hospital system required its staff of 26,000 to get COVID-19 shots, 117 workers went to court, arguing the vaccines are “experimental” and dangerous, and that forcing employees to be “human ‘guinea pigs’ as a condition for continued employment” is unethical.

A Texas federal judge on Saturday threw out the lawsuit, saying it distorted the facts. He denounced as “reprehensible” its comparison of the pandemic vaccine mandate to Nazi medical experimentation during the Holocaust.

That decision by U.S. District Judge Lynn N. Hughes — the first to address a somewhat gray legal area — is reassuring for the University of Pennsylvania Health System and the small but growing number of private employers requiring COVID-19 shots.

“I was pleased to see he came down in an opinion that was strongly worded and dismissed the lawsuit’s arguments,” said Patrick J. Brennan, chief medical officer of UPHS, the city’s biggest private employer with a workforce of 47,000.

Requiring that health care workers be vaccinated to help protect their patients and colleagues, as well as themselves, is nothing new; seasonal flu shot mandates are fairly standard.

But debates — and a few unsettled lawsuits — have swirled around the legality and ethics of COVID-19 vaccine mandates, even as evidence mounts that the three vaccines used in the United States and globally are spectacularly effective and safe. COVID-19 cases and deaths are falling in many regions, including Southeastern Pennsylvania, as vaccination rates grow.

A big sticking point is whether the vaccines are “experimental” because they were granted emergency authorization by the Food and Drug Administration, not full approval. By federal law, people must be told they can refuse or accept such a provisionally approved vaccine.

Some legal experts dismiss that argument as a red herring. And even if it is valid, both Moderna and Pfizer-BioNTech have applied for full approval, and are expected to get it soon.

What’s more, the U.S. Equal Employment Opportunity Commission issued guidance in May that said private employers can require vaccinations, as long as the requirement does not treat employees differently based on race, religion, sex, sexual orientation, pregnancy, disability, age, or genetic information.

The Penn system announced in May that all workers must be vaccinated by Sept. 1 or face possible firing. This week, the system issued application forms for those seeking exemptions.

But judging from the forms, getting one won’t be easy. Not only are serious medical reactions to the vaccine rare, but no organized religion opposes using vaccines to prevent illness. At Houston Methodist, more than 99% of workers have been vaccinated, 285 received exemptions, 332 were granted postponements for pregnancy or other temporary conditions, and 178 noncompliant workers have been suspended and could lose their jobs.

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UPHS will consider medical exemptions only for employees whose doctors document a history of severe allergic reaction (anaphylaxis has occurred with the Pfizer and Moderna vaccines) or a condition that is “recognized” to make COVID-19 vaccination risky. (A devastating blood clotting disorder has been linked to about 1 out of a million people who have gotten the J&J vaccine.) Vaccination may be postponed for people who are pregnant, undergoing chemotherapy, or within 90 days of recovery from severe COVID-19.

Religious exemptions, meanwhile, will require more than just a sincerely felt belief or opinion, especially for those who have gotten other vaccines and comply with Penn’s seasonal flu shot requirement.

“A philosophical objection is not enough,” Brennan said. “That can become more political than religious.”

Indeed, 40% of Republicans have consistently told pollsters they do not plan to be vaccinated. But lots of other factors, including mistaken beliefs and gut feelings, also play a role in vaccine hesitancy. Many frontline health care workers — people who have seen COVID-19 devastation firsthand — haven’t yet been vaccinated, polls show.

If UPHS grants a religious exemption, the worker may be assigned to another job or to extra infection prevention measures, or both, “in order to protect patients, staff, and others.” Federal law allows that.

So far, the only pushback UPHS has faced has come from some of its Lancaster General Hospital employees. They held a protest rally and a petition drive in recent weeks.

Eric Winter, a Reading-based lawyer who is advising the resistant employees, said the petition would be given to Lancaster hospital administrators on Wednesday, but he didn’t know how many workers signed it.

He insisted the employees are not against vaccines, just the COVID-19 vaccines. They want to “wait for more data,” he said, even though 173 million Americans — more than half the population — have received at least one dose.

Yet he also suggested that a bonus of time or money could overcome the need for more data.

“Most other hospitals are not making it mandatory,” Winter said. “They’re using an incentive-based system. Is there a reason Lancaster General and Penn can’t do that? Give a bonus of three extra vacation days,” or a cash bonus.

A survey of 600 employers by the labor law firm Fisher Phillips found 83% were not going to require vaccination. However, among health care employers, 3% had mandates and 29% were considering it.

In his ruling, Judge Hughes pointed out that no worker at Houston Methodist is being forced to get a vaccine.

“Methodist is trying to do their business of saving lives without giving them the COVID-19 virus,” Hughes wrote. “It is a choice made to keep staff, patients and their families safer. [The lead plaintiff] can freely choose to accept or refuse a COVID-19 vaccine; however, if she refuses, she will simply need to work somewhere else.”