"We know that the biggest risk is these closed, indoor environments," University of Maryland virologist Don Milton told Business Insider.
Milton, along with hundreds of the world's leading virus scientists and environmental engineers, is pressing the World Health Organization to better convey to the public how this virus behaves in the air.
In particular, that closed, indoor settings have played an important role in spreading the virus, and the disease it causes — COVID-19 — around the world.
Until now, the WHO has maintained that there's no evidence the virus can stay aloft in the air for very long, or travel very far in it, outside of hospital settings.
But the scientists behind this new letter warn that may not strictly be the case when you're in a stuffy space. As a result, they say, the WHO's current position that airborne transmission is not a concern for the general public is no longer air-tight.
"It's increasingly clear that these big outbreaks where lots of people get infected are one of the most important ways in which this pandemic keeps going," Milton said. "We need to stop those super spreading events, and the way to stop those super spreading events is to pay attention to airborne transmission."
The WHO has stuck to an old-fashioned definition of 'airborne'
The WHO stresses that the coronavirus does not typically float around, with the exception of a few clinical "aerosol generating procedures" in hospitals (including intubation, ventilation, and resuscitation).
"Airborne transmission is different from droplet transmission," the WHO says in its most recent guidance on the subject, because airborne virus "can remain in the air for longer periods of time, and can be transmitted to others over distances greater than 1 meter" (roughly 3.3 feet).
Why hundreds of experts are calling on the WHO to change its messaging
On Monday, Milton, and co-author Lidia Morawska, were among an international group of "239 scientists" who put their name on an open letter in the journal of Clinical Infectious Diseases, titled "It is Time to Address Airborne Transmission of COVID-19."
The letter was aimed at getting the world's biggest public health organizations "including the World Health Organization" better on board with the idea that the coronavirus spreads easily through the air from person to person — even, perhaps, up to "several meters" away across a room.
They stress that is one big reason that the pandemic virus continues circling the world, and the general public should be aware, as restaurants, bars, clubs, and offices open up.
"There's real concern that delay in pushing the idea of universal masking and talking about transmission by aerosols, airborne transmission, has put people at risk, and that there are fairly straightforward things that people could do to be safer, and to reduce the spread of the virus," Milton said.
The agency is listening, but is cautious about making big statements
On Tuesday, the WHO still said more research is needed to know for sure how this virus spreads best.
The health agency said it would be issuing a "scientific brief" on the subject in the coming days, in the wake of Milton's new letter.
"We have been engaged with this group since April, when they first wrote to us on April 1st, and we've had an active engagement with them," Maria Van Kerkhove, the WHO's technical lead for the coronavirus pandemic, said on Tuesday during a press conference from the agency's headquarters in Geneva.
But the agency is taking a very cautious approach.
"Any guidance that we put out has implications, of course, for billions of people around the world. So it has to be carefully considered before it is done," the WHO's chief scientist Soumya Swaminathan said Tuesday during the briefing. "We want to be as fast as possible, and adaptive and responding to the new evidence. And at the same time, we have to consider the weight of the evidence."
Fresh air can help make indoor spaces less dangerous
The WHO has so far maintained that this virus spreads best when people cough, talk, breathe, and sneeze out droplets — viral particles that are hundreds of times smaller than a human hair, but much larger and heavier than aerosols, which float in the air.
Droplets spread from person to person through close contact, especially when people are together for extended periods of time.
From a layperson's viewpoint, it may not seem that important to know whether the virus spreads through droplets or aerosols, they're both tiny little doses of virus.
But the distinction subtly changes your perception of how risky everyday actions really are, and may change how close people decide to get to others when indoors during the pandemic.
Give the public better information about the powers of crowd control, masks, and airflow
Better crowd control, more masking, and paying close attention to air quality in closed, heavily-trafficked spaces, are three critical ways to stop this virus, as we continue to learn more about how it spreads best, and make mundane decisions about how to proceed with everyday life, in the absence of a vaccine.
"We have to learn to live with this virus," the WHO's executive director of health emergencies, Mike Ryan, said last week, encouraging "every person" in the world to "take control of your own destiny."
Likewise, Dr. Anthony Fauci, the US's top infectious disease expert, told members of Congress last week that "we need to emphasize the responsibility that we have both as individuals and as part of a societal effort to end the epidemic — that we all have to play a part in that."
If the general public is paying closer attention to air flow, crowding, and wearing masks, this will all be easier.
"It's really trying to grapple with what we know is happening and doing very simple, straightforward things that we can do that can stop the spread of this virus," Milton said.
"By not having too many people sharing the same air, and by not putting a lot of virus into that air, we can keep these events from happening."
But Milton and his colleagues are worried that the WHO's current message leaves out some "fairly straightforward" ways that we've seen the virus being transmitted in recent months, especially when big crowds gather indoors. They stress there's room for some more precautions, in conjunction with the handwashing, social distancing, mask wearing, and quarantining recommendations already in place.
"We're not saying that the things that have been recommended are wrong, we're just saying there's more stuff to be done, and that it's important for people to know about it," Milton said.
3 ways to prevent super spreading events
According to Milton, three measures are key to prevent transmission of a virus that "needs a lot of people, breathing the same air, and ... somebody contaminating that air with virus."
- Making sure indoor spaces are more well-ventilated, including opening up windows and doors to bring in outdoor air, and maintaining good air filtration in closed spaces, minimizing recirculating air.
- Avoiding overcrowding in public spaces.
- Using germicidal UV lights overhead to kill the virus. (Milton's lab uses these in places where researchers work with people who have the coronavirus, and he's not worried about any of them getting infected.)
