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About 50 employees of Essentia Health, an upper-Midwest hospital chain, didn’t go to work Wednesday.

But it wasn’t an early start to the Thanksgiving holiday for them. They were fired for refusing to get flu shots.

It’s part of a growing trend for hospitals to require flu shots for workers. Public health experts say it shouldn’t be surprising.

Flulapalooza tent, an attempt at Guinness Book of World Records. Susan Urmy / Vanderbilt

“It’s a patient safety issue,” said Dr. William Schaffner, an infectious disease expert at Vanderbilt University and a spokesman for the Infectious Diseases Society of America. “It’s so that we do not give flu to our patients.”

Hospital workers can pass the flu virus to some of the most vulnerable people — frail elderly, babies in incubators, patients with immune systems ravaged by cancer treatment. Vaccinating employees protects patients and the employees’ co-workers.

Related: Hospital gets workers vaccinated with in-your-face flu campaign

“Patients are in the hospital because they are sick,” said Dr. Rajesh Prabhu, Infectious Disease and Chief Patient Quality and Safety Officer at Essentia Health. "That puts them at risk of a more severe outcome from influenza. People can die from influenza.”

Each year, influenza virus kills between 4,000 and 50,000 Americans, including children who were perfectly healthy before they caught flu.

Just about everyone is advised to get a flu vaccine. The Centers for Disease Control and Prevention recommends annual flu vaccines for everyone of the age of 6 months who doesn’t have a medical reason not to — for instance, an allergy to the vaccine.

“It’s so that we do not give flu to our patients.”

But vaccination rates are low, and even among healthcare workers, only around 65 percent get flu vaccines every year, the CDC says.

Requiring the vaccine gets those rates up, protects patients and causes no harm, Schaffner said.

When employers require the vaccine, the CDC found, 85 percent of workers get one. Just 43 percent get vaccinated if there is no policy.

Related: Caterpillar-grown flu vaccine works better

Several states, including California, require hospitals to make flu vaccines mandatory and to record and publish their vaccination rates. Maryland has a searchable database telling people a hospital’s vaccination rate.

Minnesota doesn’t require this but Essentia said it started the mandatory policy to protect patients.

“Just like other people, we had a voluntary program really encouraging our health care personnel to get vaccinated,” Prabhu said.

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“In 2012-2015 our vaccination rate among health care workers was about 70 percent.” That’s not good enough, he said. “The last flu season, we went to mandatory participation. Everyone who worked at Essentia had to say yes or no.” That got vaccination rates to 82 percent — still not good enough.

Now, Essentia employees must either be vaccinated or go through a process similar to school enrollment requirements: they must apply for a medical or religious/philosophical waiver. The requests are reviewed by expert committees.

That’s gotten the compliance rate to 99.5 percent, Essentia spokeswoman Maureen Talarico said. The hospital system does not have a clear vaccination rate yet.

Employees were given extra time to start the review process if they objected to getting a vaccine, but after an extra month, Monday was the cutoff for either getting a vaccine, or for starting the opt-out paperwork.

“We were vaccinating on Monday,” Talarico said.

Like many hospital systems, Essentia offered multiple free vaccine clinics, had vaccine carts available to go to workers so they did not have to take the time to line up or seek out a flu shot and made sure every floor or unit had someone certified to administer vaccines.

“You cannot get to a high immunization rate without some kind of mandatory flu vaccination program,” Prabhu said.

“We had a cutoff of November 20. If they did not participate in the process, they would no longer be allowed to work at Essentia Health.”

Out of nearly 14,000 employees, only about 50 took it to that point, Essentia said.

Related: Why flu vaccines aren't so hot

No opt-out except for medical

Influenza is not the only vaccine that’s required for health care workers. Hepatitis B, measles, mumps, rubella, diphtheria, tetanus, chickenpox and whooping cough vaccines are also required, Prabhu said.

Hand hygiene is also enforced, Prabhu added.

The Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the Pediatric Infectious Diseases Society and other groups all support mandatory immunization of health care workers — and all say there should be no opt-out except for medical reasons.

This is, in part, because people infected with influenza can pass it to others both before they have symptoms and after they feel better. In addition, people who think they just have the sniffles may in fact have flu and can pass it around.

"If they did not participate in the process, they would no longer be allowed to work at Essentia Health.”

“Obviously, it is also about personal protection,” Schaffner said.

“We want them to be protected because during a flu outbreak we need our healthcare personnel to be vertical rather than horizontal. We need them fit and able to care for all the people who need care,” Schaffner added.

Vanderbilt doesn’t fire people who refuse vaccination, but makes them undergo counseling and then wear a mask during flu season.

And they made vaccination into a party they called “Flu-la-palooza”. “It’s a one-day event brilliantly organized to throughput as many people as quickly and easily and appropriately as possible,” Schaffner said.

“This year we did almost 14,000 people.”

In fact, the medical center now holds a Guinness World Record for the event.

Schaffner said it had an added benefit.

“It’s a training process such that if there is a pandemic and we have to vaccinate very large numbers of our people, our personnel and our administrative people are beautifully trained,” Schaffner said.

Why would any health care worker refuse to get a flu vaccine?

Prabhu and Schaffner said health care workers have the same arguments that non-medical people do —they’re afraid of side-effects, even though side-effects are not as serious as people believe they are; they think they don’t need the vaccine because they “never” get flu; or they worry it’s a waste of time because flu vaccines do not always provide perfect protection.

“We all know it has limitations and we all recognize that it is the best that science has to offer us at this point,” Schaffner said.

He quotes an old saying about not letting the goal of perfection undermine doing good.

“We can all do a lot of good with our pretty good vaccine,” he said.