“The most common way COVID-19 is transmitted from one person to another is through tiny airborne particles of the virus hanging in indoor air for minutes or hours after an infected person has been there,” Alondra Nelson, head of the White House Office of Science and Technology Policy, wrote in a blog post last week. “While there are various strategies for avoiding breathing that air — from remote work to masking — we can and should talk more about how to make indoor environments safer by filtering or cleaning air.”

The Biden administration’s turn toward improving ventilation comes as experts focus on new ways of managing a pandemic that continues to challenge global leaders more than two years after the virus first emerged. Its recommendations range from simple tactics, such as propping open doors and windows, to more complex investments to upgrade ventilation systems by installing better filters and portable cleaners, with officials urging building operators to tap funds previously made available through coronavirus stimulus packages.

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As state and local leaders roll back vaccination and mask mandates, experts say improving indoor air quality is increasingly essential as a tool to contain coronavirus risks.

“It’s important that this becomes a passive control measure — passive in the sense that it doesn’t require people to do anything,” said Joseph Allen, director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health. “It’s not requiring you to wear a mask, or wear a good mask or wear it right. It’s operating in the background all the time.”

Although scientists hailed the White House’s moves, they said they were frustrated that the Centers for Disease Control and Prevention and the World Health Organization, among other groups, had initially resisted warnings that the virus was spreading through microscopic particles that can hang in the air long after an infected person has departed.

“This is a total rejection” of earlier assumptions that the virus was spread through direct contact between individuals, said David Michaels, a George Washington University professor who previously led the Occupational Safety and Health Administration and advised Biden’s transition team on the coronavirus pandemic. “I think much of the world has been dragged kicking and screaming into this because the World Health Organization and the CDC both clung to the infectious-disease model.”

The CDC, the WHO and other groups initially maintained that the virus mostly spread in large droplets that fell to the ground within a few feet of the person expelling them, probably through a cough or a sneeze. But research has shown that it is often transmitted through the air in far smaller and more numerous particles that are aerosolized and, therefore, can travel distances — and require very different approaches to managing.

The White House telegraphed its growing focus on air quality in a coronavirus response plan released on March 2, following Biden’s State of the Union address. The Environmental Protection Agency earlier this month also announced its Clean Air in Buildings Challenge, a tool kit for how building owners and operators can ensure more healthful air, such as by circulating clean outdoor air indoors and installing better air filtration devices. The Biden administration has yet to craft regulations, however, or provide additional funding that experts say is needed.

Administration officials said improvements are underway, noting that schools have already spent billions of dollars in coronavirus stimulus funds to upgrade ventilation systems.

“We really did want to raise this up as a priority,” said Mary Wall, a senior adviser on the White House coronavirus response team, pointing to the EPA tool kit and pledging that more initiatives are forthcoming. “We know this is long work that takes time.”

In interviews, four scientists involved with the White House’s event on Tuesday lamented missed opportunities earlier in the pandemic to highlight the link between the virus and indoor air quality. More than 200 scientists in July 2020 called on the WHO and other global health bodies to acknowledge the risk that the coronavirus could spread by air — a petition that for months was largely ignored.

“We should have done it earlier,” said Linsey Marr, an environmental engineer at Virginia Tech who was among the first scientists to warn in 2020 that the coronavirus was spreading by air. “But, as far as this effort led by the White House, it’s better late than never.”

The CDC in October 2020 first acknowledged “limited, uncommon circumstances” when people were infected with the virus through airborne transmission, particularly in enclosed spaces with inadequate ventilation. Later, in May 2021, the agency revised its guidance to emphasize that airborne transmission was a significant driver of infection.

But, for much of the pandemic, health officials highlighted measures such as social distancing and wearing cloth masks that may defend against large droplets but offered far less protection against aerosols.

Meanwhile, scientists said, leaders could have done more to prop open windows, adjust HVAC systems to use more outdoor air, add portable HEPA air cleaners and take other immediate steps to improve indoor air quality and mitigate risks as soon as the summer of 2020, when evidence on the virus’s airborne spread was first apparent.

Tuesday’s White House event featured experts including Marr, Allen and Zeynep Tufekci, a University of North Carolina sociologist who has written extensively on how the virus can be transmitted by air, who shared their findings. Officials also spoke on the need to tailor air quality goals and standards to different environments.

“We have unique challenges when we’re addressing indoor air quality in schools,” said Tracy Enger, a program manager at EPA. Compared with adults, she added, children “breathe deeper and faster, so they’re more vulnerable and more susceptible to a lot of the exposures. They have hand-to-mouth activities. They are what one of my friends calls ‘belly botanists.’”

Michaels, the former OSHA head, said the benefits of the change in focus would include curbing the risk of other respiratory diseases.

“It makes clean indoor air a priority, just like clean water,” Michaels said.

The hospital industry, he said, has “always fought against having to treat infectious disease as airborne because they put people in rooms for the most part, put a curtain around them and put someone else in the bed 10 feet away, and they think the curtains are going to protect people.”

The White House “is saying that that’s not going to work,” he added.

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