Employers piece together a hodgepodge of COVID-19 safety policies to stay open and healthy

“Employers are trying to navigate this as best they can because they obviously want employees to feel comfortable coming into the office,” she said.

The Centers for Disease Control and Prevention and the US Department of Labor have issued general guidance for employers. They include regular testing, masking, and physical distancing for workers who are not fully vaccinated, and a recommendation that everyone, vaccinated or not, wear masks in public indoor settings in regions where transmission is still high.

But devising one, uniform COVID safety plan has been challenging, because of the variety of workplace settings, from small mom-and-pop stores, to large warehouse operations, to giant corporations with a multistate footprint, Lee said. And that’s in addition to having to take into account varying local, state, and federal COVID rules and virus transmission risk levels that change from one county to the next.

And companies are tackling this while still trying to formalize new hybrid work schedules, with some employees still fully remote and others in the office several days a week. A recent national survey of company executives by Littler, an employment law firm, found roughly half had workers back in the office at least part time, while another 13 percent planned to return by August. The rest either had no established return date by August; did not have any employees working remotely; or had shifted permanently to remote work.

“It’s hard to have a one-size-fits-all version,” said Jonathan Levy, chair of the department of environmental health at Boston University’s School of Public Health.

He said COVID testing is an important tool to help keep infected people out of the workspace. But the tricky question is how often to test, because it depends on the setting, how many people are in the space, and the nature of the work.

“That’s why you need a ‘Swiss cheese model,’” Levy said.

That means it’s not realistic to test frequently enough to have that be a company’s only protection, Levy said. Employers also need to ensure good ventilation or upgraded filtration for heating and cooling systems, because COVID is typically transmitted by airborne droplets called aerosols.

“Maybe you have portable filters or windows you can open,” he said. “Whatever strategy works, because having better ventilation actually increases worker productivity.”

The bottom line, public health experts say, is that employers need to be flexible, because COVID is expected to continue to wax and wane. Corporate policies may require masks and more remote work during times of high transmission.

Amid that kaleidoscope of factors, Lyndra Therapeutics crafted a multipronged approach for its 152 employees in Watertown and Lexington that requires all employees to be vaccinated and to undergo COVID testing at least twice a week, with PCR tests provided by the company. Employees swab themselves at work, and the company sends the batches out, with results generally in less than 24 hours.

Masks are optional but the company uses a color-coded bracelet system that allows workers to convey their preference. Workers wear a green bracelet if they are comfortable with colleagues going maskless around them; yellow if they are wearing a mask but don’t expect others to; and red if they want those in their vicinity to mask up.

“Most people wear yellow or green bracelets,” said Trish Hurter, Lyndra’s chief executive. “I have not seen too many reds.”

Lyndra also uses sensors on employees’ company ID badges that help managers instantly identify workers who were within 6 feet for more than 15 minutes of a colleague who tested positive. The sensors download the information to a database to help managers notify workers who may have been exposed.

Plotting COVID office strategy is even more complex for such companies as Wayfair, an online retailer headquartered in Boston with about 4,500 workers, but thousands more in warehouses and other offices spread across the country and in Europe.

For instance, Wayfair requires vaccination for employees in its headquarters and other offices, but not in its warehouses, where workers are less likely to be in close contact and are more likely to push back on that rule.

There are different rules for testing as well. Office workers are tested about twice a week in pooled samples, and if a batch indicates a positive sample, everyone in that batch is retested and must work from home for a day until they are cleared.

But warehouse workers are individually swabbed for a faster turn-around time.

“These team members have to be on the ground, moving boxes, so losing the 24 hours for everyone in a pool (batch) is not sustainable,” said Kate Gulliver, Wayfair’s chief people officer.

Masking is optional in Wayfair offices, but in warehouses, where many workers may not be vaccinated, masks are required when community transmission levels of the virus are deemed high risk by the CDC and workers start testing positive.

“That means we need to be flexible,” Gulliver said. “We may need to have masks and then drop masks.”

One issue that companies have increasingly had to deal with since most federal and state mask rules have ended is “mask shaming,” with some workers ridiculing others who continue to use face coverings, said Lee, from the human resource association.

Erin Britt, a spokeswoman for CVS Health, with 12,000 employees in Massachusetts and about 300,000 nationwide, put it this way: “We have communicated to all of our employees that we support employees wearing masks at work, if they feel comfortable doing that.”

Masks are only required for employees in their Minute Clinics, she said.

Most companies have a plan for alerting workers who may have been exposed to a colleague who tested COVID positive, calling or e-mailing those affected. But they must be discreet because federal privacy rules restrict employers from sharing personal health information about any employee.

The CDC recommends that unvaccinated people and those not yet boosted who are exposed to an infected person quarantine for five days, followed by strict mask use for an additional 5 days. If quarantining is not feasible, the CDC says a person should wear a well-fitting mask at all times around others for 10 days after exposure.

The agency says people who have received a booster shot do not need to quarantine following an exposure but should wear a mask for 10 days after the exposure.

As the number of reported COVID cases and hospitalizations ease in Massachusetts, employers are finally exhaling a bit. But given all the curve balls the pandemic has thrown, many remain cautious.

“COVID is different than anything else we in the workplace have ever seen,” said Lee, from the human resource association. “Employers are now thinking, ‘What can we do if something similar comes around again?’”

Kay Lazar can be reached at kay.lazar@globe.com Follow her @GlobeKayLazar.