As COVID cases drop in the U.S. and vaccinations increase, many companies are bringing their employees back to office buildings. And lots of those workers are worried: Will shared spaces remain safe as restrictions are lifted and viral variants spread? Can businesses require all employees to be vaccinated? What office and building features best minimize risk? To get answers, Scientific American asked experts in infectious disease, air-flow engineering, and the law to explain the office designs and policies that will most improve coronavirus safety and the ways you can evaluate these factors.

If you’re vaccinated, you can return to work as normal (mostly).

The most effective way to reduce the spread of the coronavirus at work is to make sure that everyone in the shared space is vaccinated. Current guidelines from the Centers for Disease Control and Prevention specify that fully vaccinated people (those who are two weeks past their final vaccine dose) no longer need to wear a mask or practice physical distancing in most situations, including most office workplaces.

COVID vaccines are highly effective at preventing infection and illness, so once you are fully vaccinated, “it doesn’t really matter what the vaccine status is of those around you,” says Gretchen Snoeyenbos Newman, an infectious disease physician at Wayne State University. If you’re returning to a workplace where some of your co-workers are unwilling or unable to get vaccinated or to wear a mask, the best protection you have is getting immunized yourself, she says.

Workers who are unvaccinated or otherwise vulnerable need masks, distancing and adequate ventilation.

Unvaccinated people should wear a mask around others who are not in their immediate household (which is usually the case for those in an office), stay six feet apart in public spaces, and avoid crowds and poorly ventilated spaces, according to the CDC. A minority of people have chosen not to get vaccinated, leaving themselves open to infection and others near them in jeopardy. But some people remain unvaccinated for reasons beyond their control—they don’t have vaccine access or they have health conditions that prevent them from getting a shot. Still others are immunocompromised and may not get full vaccine protection. These workers all require added precautions, says Syra Madad, a special pathogens expert at NYC Health + Hospitals. If your office includes a mix of people who are vaccinated and unvaccinated, then your company needs to use these risk reduction measures, she says.

Partial barriers do not make cramped offices safer.

SARS-CoV-2, the virus that causes COVID, travels through the air in tiny aerosolized particles. It is not enough to erect plexiglass barriers that cover a few square feet between desks if you are going to be sharing that confined space for an entire workday. Plexiglass shields are good for instances where people are having short face-to-face interactions, such as at a bank teller’s window or a ticket office, says Linsey Marr, an environmental engineer at Virginia Tech. But those dividers make little difference if you are spending hours in a shared space because exhaled viral particles can build up over time, making the air more infectious. There is also a danger that such barriers will impair ventilation currents that would otherwise clear the air. One recent study in Science showed that in schools, the use of partial shields around desks was associated with more COVID cases, Marr says, most likely because of this problem.

Good ventilation is more important than surface cleaning.

“There’s a lot of hygiene theatre out there,” Marr says. “Regular surface cleaning is good, but cleaning the air is much more important for reducing the risk of transmission of this virus.” Almost all COVID infections are picked up through indoor air transmission. Avoid spraying disinfectants in the air, Marr says, because they can be harmful when inhaled. Instead “ventilation and filtration are the two best tools that we have to reduce the risk,” she says.

Before returning to your office, find out how often the building’s ventilation system completely blows out indoor air and takes in fresh air from outside. “You’re looking for at least three to four air changes per hour—meaning that every 15 to 20 minutes, the indoor air is replaced with outdoor air,” Marr says.

Next, she says, you should find out the MERV (minimum efficiency reporting value) number of the HVAC (heating, ventilation and air conditioning) filter. Higher is better, and your office’s filter should have a rating of at least 11. That number corresponds to a filter that can remove about 90 percent of particles that are one micron in size. (It is harder to push air through the filters with higher MERV numbers, so not all systems can function with them.)

It may be difficult to find someone at your company who can give you this information. An alternative is to measure the carbon dioxide in the office. “Carbon dioxide level is an indicator of exhaled breath. So if the level is high, it means that there’s a lot of exhaled breath hanging around in the air,” Marr says. “You’re looking for a number below 800 parts per million, or ppm.” She notes that it’s possible to buy a decent handheld CO2 sensor around the size of a phone for about $200. “Many of the experts on aerosols and transmission carry these around,” she says. “When I see a high number, I know I should not spend a lot of time in there.”

Marr makes an exception to her 800-ppm rule in buildings with good air filtration. “As long as the particles in the air are being removed by a good filter, then your carbon dioxide level can be higher than that 800 number,” she says.

Consider a portable air filter.

Portable air filters can be purchased for around $200 to $300 and can filter a small room, Marr says. They can range in size from a small desktop device to a larger unit that sits on the floor, depending on the area it is intended to serve. Such a tool could be useful in a confined conference room, for instance. “Look for something with a high-efficiency particulate air (HEPA) filter,” she says, because such filters are certified to remove at least 99 percent of particles of all sizes. “They’ll try to sell you ones with UV or fancy metals or ionization or some other method to kill a virus,” she says, but such add-ons are unnecessary (and, in some cases, unproved or ineffective). A recent CDC study found that using HEPA air filters reduced the aerosol exposure of people in a room by up to 65 percent. The filters worked best if they were located in the center of the room, close to the aerosol source. (Adding masks in addition to the filters reduced exposure by up to 90 percent.)

It is legal for your employer to require vaccinations (usually).

Under federal equal employment opportunity laws, employers can mandate vaccinations for their workers, and they are allowed to require proof, says Sharon Rennert, a senior attorney adviser for the U.S. Equal Employment Opportunity Commission. But Rennert also notes that some states have passed laws or enacted executive orders prohibiting these practices. Because federal law does not explicitly require vaccine mandates, the state laws have authority in this area. The National Academy for State Health Policy tracks state health legislation and notes that as of early July, six states had banned vaccine mandates or the use of vaccine passports. About 120 different bills on these issues had been introduced in states across the nation.

Some privacy about vaccination status is protected.

Although it is legal for your employer to ask about your vaccination status, it is not legal, under the Americans with Disabilities Act (ADA), for them to share this information in most circumstances. You can discuss your status with your colleagues if you feel comfortable doing so, however, Rennert says. There is a common misconception that asking about someone’s vaccination status is a violation of the Health Insurance Portability and Accountability Act (HIPAA), but this is incorrect.

Vulnerable employees are entitled to safety measures.

The ADA gives workers with certain conditions a legal right to reasonable accommodations to protect them from contracting COVID. People with a compromised immune system or diabetes, for instance, merit such protection. “‘Reasonable accommodation’ is a very flexible requirement, meaning that you really look at the specific circumstances of this employee's workplace to determine what would be appropriate,” Rennert says. Protections might include things such as a private work space that is physically isolated from co-workers, staggered hours to reduce exposure to other people or a work-from-home arrangement. (Rennert notes that the ADA requires accommodations if the employee is the one with a vulnerability but not if the vulnerable person is someone in their household.)

Policies for quarantine and sick leave are essential.

The federal Occupational Safety and Health Administration advises that your employer allow you to stay home if you are infected with SARS-CoV-2 or if you are unvaccinated and have had close contact with someone who has tested positive for COVID. The guidelines state that policies should be “non-punitive” and should not encourage workers to come in sick or when they have been exposed to the virus (if they are unvaccinated).

You have the legal right to report any worries about COVID safety.

The Occupational Safety and Health Act of 1970 prohibits retaliation for voicing concerns about workplace safety or health concerns. And OSHA guidelines encourage employers to establish a hotline or other method for workers to anonymously report concerns they have regarding COVID policies and practices.

COVID trends in your community matter.

Rates of COVID have fallen significantly in most parts of the U.S. since last fall, but there are still pockets where cases are increasing, says Joshua Weitz, a quantitative biologist at the Georgia Institute of Technology. His team has built a tool that can estimate the probability that someone in a group is infected, given the size of the group and the number of circulating cases in that area. Select your county, plug in the number of people in your office, and the tool provides an estimate of the risk that someone in the group will have COVID.

Weitz’s group has made another tool that estimates what proportion of each state’s population has immunity to the disease, either via vaccination or a natural infection. Taking these two estimates together can give you a picture of how likely you might be to encounter SARS-CoV-2 at your office.

A caution: Saskia Popescu, an infectious disease epidemiologist at George Mason University, notes that your workplace might not be a perfect microcosm of what is going on in your community. That is why you need to pay attention to company policies about vaccination and physical separation and office features such as ventilation and filtration. Plus, with both people and circulating viral variants traveling at increased rates, the local picture could change very quickly.

It is okay to feel worried about all of this.

“The last 18 months have been really traumatic,” Newman says. Having some fear around returning to normal is understandable. “It’s okay to give ourselves permission to be kind of anxious about returning to life in a more contact-filled world,” she says. Shared offices are just one aspect of that life. Newman and her wife recently had their first indoor meal at a restaurant since the pandemic began, and she says that before they went in, “we took a deep breath.”

Editor’s Note (8/2/21): This article has been edited after posting to clarify the laws relevant to employer vaccination mandates and privacy.