Employers are trying to make sure that employees feel comfortable in 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.

The variety of workplace settings, from small mom-and-pop stores, to large warehouse operations, to giant corporations, has made it difficult to come up with a uniform safety plan. It is necessary to take into account different 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.

Jonathan Levy, chair of the department of environmental health at Boston University, said it was difficult to have a one-size-fits-all version.

He said that it is important to keep people out of the workspace. How often to test depends on a number of factors, such as the setting, the nature of the work, and how many people are in the space.

Levy said that you need a “Swiss cheese model”.

Levy said that it is not realistic to test frequently enough to have that be a company’s only protection. COVID is typically transmitted by airborne droplets called aerosols, so employers need to make sure their heating and cooling systems have good ventilation and upgraded filters.

He suggested that you have portable filters or windows that you can open. Having better ventilation actually increases worker productivity, so whatever strategy works.

According to public health experts, employers need to be flexible because COVID is expected to continue to wax and wane. During times of high transmission, corporate policies may require masks and more remote work.

In response to that kaleidoscope of factors, the company created a multipronged approach for its employees that requires all of them to be vaccinations and to be tested at least twice a week. In less than 24 hours, the company will send out the batches of saliva from the employees.

The company uses a color-coded bracelet system that allows workers to say what they want. 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 bracelets that are yellow or green. I have not seen lots of reds.

Managers can instantly identify workers who were within 6 feet for more than 15 minutes of a colleague who tested positive by using sensors on their company ID badges. Managers can notify workers who may have been exposed by using the information from the sensors.

It’s even more difficult for companies like Wayfair, an online retailer with about 4,500 workers in Boston, and thousands more in warehouses and other offices across the country and in Europe, to plan coherent offices.

In its warehouses, workers are less likely to be in close contact with each other and are more likely to push back on a rule that requires vaccinations for employees.

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

The workers are tested individually for a faster turn-around time.

Losing 24 hours for everyone in a pool is not sustainable because the team members have to be on the ground.

When community transmission levels of the virus are deemed high risk by the CDC and workers start testing positive, masks are required in warehouses where many workers don’t have a vaccine.

We need to be flexible, that’s what it means. We might need to 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.

“We have communicated to all of our employees that we support employees wearing masks at work if they feel comfortable doing that,” said a spokeswoman for CVS Health.

She said that masks are not required for employees in Minute Clinics.

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 don’t need to wear a mask, but should wear one for 10 days after exposure.

Employers are starting to exhale as the number of reported COVID cases and hospitalizations decreases in Massachusetts. Many remain cautious because of the curve balls thrown by the Pandemic.

According to Lee from the human resource association, correlation is different than anything else they have ever seen. Employers are wondering if they can do anything if something similar comes around again.

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