Nearly a year after scientists showed that the coronavirus can be inhaled in tiny droplets called aerosols that linger indoors in stagnant air, more than a dozen experts are calling on the Biden administration to take immediate action to limit airborne transmission of the virus in high-risk settings like meatpacking plants and prisons.

The 13 experts — including several who advised President Biden during the transition — urged the administration to mandate a combination of masks and environmental measures, like better ventilation, to blunt the risks in various workplaces.

On Friday, the Centers for Disease Control and Prevention issued new guidelines for reopening schools, but quickly passed over improved ventilation as a precaution. It was only in July that the World Health Organization conceded that the virus can linger in the air in crowded indoor spaces, after 239 experts publicly called on the organization to do so.

In a letter to the administration, scientists detailed evidence supporting airborne transmission of the virus. It has become even more urgent for the administration to take action now, the experts said, because of the slow vaccine rollout, the threat of more contagious variants of the virus already circulating in the United States, and the high rate of Covid-19 infections and deaths, despite a recent drop in cases.

“It’s time to stop pussyfooting around the fact that the virus is transmitted mostly through the air,” said Linsey Marr, an expert on aerosols at Virginia Tech.

“If we properly acknowledge this, and get the right recommendations and guidance into place, this is our chance to end the pandemic in the next six months,” she added. “If we don’t do this, it could very well drag on.”

The letter was delivered on Monday to Jeffrey D. Zients, coordinator of the Biden administration’s Covid-19 response; Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention; and Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.

The letter urged the C.D.C. to recommend the use of high-quality masks, such as N95 respirators, to protect workers at high risk of infection. At present, health care workers mostly rely on surgical masks, which are not as effective against aerosol transmission of the virus.

Many workers vulnerable to infection are people of color, who have borne the brunt of the epidemic in the United States, the experts noted.

Mr. Biden has directed the Occupational Safety and Health Administration, which sets workplace requirements, to issue emergency temporary standards for Covid-19, including those regarding ventilation and masks, by March 15.

But OSHA will only mandate standards that are supported by guidance from the C.D.C., said David Michaels, an epidemiologist at George Washington University and one of the signatories.

(Dr. Michaels led OSHA during the Obama administration; the agency has not had a permanent leader since his departure.)

“Until the C.D.C. makes some changes, OSHA will have difficulty changing the recommendations it puts up because there’s an understanding the government has to be consistent,” Dr. Michaels said. “And C.D.C. has always been seen as the lead agency for infectious disease.”

Public health agencies, including the W.H.O., have been slow to acknowledge the importance of aerosols in spreading the coronavirus. It was only in October that the C.D.C. recognized that the virus can sometimes be airborne, after a puzzling sequence of events in which a description of how the virus spreads appeared on the agency’s website, then vanished, then resurfaced two weeks later.

But the agency’s recommendations on workplace accommodations did not reflect this change.

Early in the pandemic, the C.D.C. said health care workers did not need N95 respirators, and could even wear bandannas to protect themselves. It also did not recommend face coverings for the rest of the population.

The agency has since revised those recommendations. It recently recommended that people wear two masks or improve the fit of their surgical masks to protect from the virus.

“But they don’t talk about why you need a better fitting mask,” said Dr. Donald Milton, an aerosol expert at the University of Maryland. “They’re acknowledging the importance of breathing it in and the route of transmission, and yet they don’t say it clearly in their various web pages.”

The agency recommends surgical masks for health care workers and says N95 respirators are needed only during medical procedures that generate aerosols, like certain kinds of surgery.

But many studies have shown that health care workers who have no direct contact with Covid-19 patients are also at high risk of infection and should be wearing high-quality respirators, said Dr. Céline Gounder, an infectious disease specialist at Bellevue Hospital Center in New York and an adviser to Mr. Biden during the transition.

“The C.D.C. has not emphasized the risk of aerosol transmission enough,” Dr. Gounder said. “Unfortunately, concerns about supply continue to muddy the discussion.”

Many hospitals still expect their staff to reuse N95 masks per the agency’s recommendation to reuse when supplies are low. But since the masks are no longer in short supply, the agency should change its recommendations, Dr. Gounder said.

“We really do need to stop this reuse and decontamination approach to N95s,” she added. “We’re a year into this, and that’s really not acceptable.”

Hospitals, at least, tend to have good ventilation so health care workers are protected in other ways, the experts said. But in meatpacking plants, prisons, buses or grocery stores, where workers are exposed to the virus for long periods of time, the C.D.C. does not recommend high-quality respirators, nor does it endorse upgrades to ventilation.

“If you go to other workplaces, this idea that aerosol transmission is important is virtually unknown,” Dr. Michaels said. In food processing plants, for example, a refrigerated environment and the lack of fresh air are ideal conditions for the virus to thrive. But the industry has not put in safety measures to minimize the risk, he added.

Employers instead hew to the C.D.C.’s recommendations for physical distancing and cleaning surfaces.

The recent emergence of more contagious variants makes it urgent for the C.D.C. to address airborne transmission of the virus, said Dr. Marr of Virginia Tech. Germany, Austria and France now mandate N95 respirators or other high-quality masks in public transportation and shops.

Dr. Marr was one of the experts who wrote to the W.H.O. last summer to push for an acknowledgment of airborne transmission. She did not expect to be in a similar position again so many months later, she said: “It feels like Groundhog Day.”