Is coronavirus airborne? WHO waits for more evidence as scientists grow impatient

Public health agencies have stayed true to their messaging on how to best protect yourself during the coronavirus pandemic: Maintain distance from others, wash your hands and wear a face mask.

The suggestions are based on evidence that the virus spreads primarily through droplets emitted from coughs and sneezes and from physical contact with surfaces that may harbor tiny viral particles.

Now, a group of 239 scientists in 32 countries are saying the World Health Organization and most other public health agencies are putting the public at risk by leaving out an important route of transmission: through the air.

One expert said the WHO interprets “an absence of evidence as evidence of absence,” Dr. William Aldis, a public health professor at Thammasat University in Thailand and “longtime WHO collaborator,” told The New York Times.

“We are concerned that the lack of recognition of the risk of airborne transmission of COVID-19 and the lack of clear recommendations on the control measures against the airborne virus will have significant consequences,” the group of scientists wrote in an open letter published Monday in the journal Clinical Infectious Diseases.

“People may think that they are fully protected by adhering to the current recommendations, but in fact, additional airborne interventions are needed for further reduction of infection risk.”

Studies on past respiratory viruses such as the Middle East Respiratory Syndrome (MERS) and respiratory syncytial virus (RSV) have shown that airborne viruses can be found in indoor environments where infected patients spend their time, and later inhaled by healthy individuals, the group said.

That happens when mucousy droplets shoot out from people’s mouths when coughing, sneezing, talking and even breathing, some studies have found.

But the WHO still reports that such droplets are “relatively heavy, do not travel far and quickly sink to the ground,” therefore rejecting the idea to some degree that airborne transmission plays a recognizable role in COVID-19 spread.

The agency also says airborne spread is only likely when certain procedures such as taking out a ventilation tube from an infected patient are done in hospitals.

In a Tuesday briefing in Geneva, WHO’s technical lead on COVID-19 Dr. Maria Van Kerkhove said they “had an active engagement” with the group of scientists that wrote the letter, NBC News reported.

Scientists conducting studies on how the virus spreads say these droplets can remain small enough to float in the air and travel great distances — as far as 12 feet in some cases — before falling to the ground.

Airborne transmission was likely behind the superspreading events among members of a Washington state choir, an apartment building in Hong Kong and a restaurant in Wuhan, China.

What’s not clear is how critical droplet size is in coronavirus spread, Donald Milton, a professor of environmental health at the University of Maryland and one of the leaders of the group behind the open letter, told CNN.

“I guess we are hoping that WHO will come around and be more willing to acknowledge the important roles of aerosols, whether they want to call it airborne transmission or not,” Milton said.

Is current guidance enough?

Current guidance on hand washing and social distancing “are appropriate, but in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people,” the letter read.

The group suggests these protective measures in addition to those touted by agencies today: “sufficient and effective ventilation” by opening windows to allow outdoor air flow, “particularly in public buildings, workplace environments, schools, hospitals and aged care homes,” high efficiency air filtration and “germicidal ultraviolet lights,” as well as the avoidance of crowded areas.

Other scientists outside of the group that wrote the letter agree there is a communication error on WHO’s behalf in an attempt to be overly cautious to claim something as fact when evidence isn’t as clear as they’d like it to be.

“There is no incontrovertible proof that SARS-CoV-2 travels or is transmitted significantly by aerosols, but there is absolutely no evidence that it’s not,” Dr. Trish Greenhalgh, a primary care doctor at the University of Oxford in Britain, told the Times.

“So at the moment we have to make a decision in the face of uncertainty, and my goodness, it’s going to be a disastrous decision if we get it wrong,” Greenhalgh said. “So why not just mask up for a few weeks, just in case?”

But there are others that believe airborne transmission shouldn’t be paid too much attention.

“Aerosol transmission can occur but it probably isn’t that important in the grand scheme of things. It’s all about droplets,” Paul Hunter, a professor in medicine at the University of East Anglia in England and a member of the WHO’s infection prevention committee, told the Guardian.

“Controlling airborne transmission isn’t going to do that much to control the spread of COVID-19. It’s going to impose unnecessary burdens, particularly in countries where they don’t have enough trained staff or resources already.”

The WHO said it is looking into more ways COVID-19 is spread, but the group asserts that the time is now to address airborne transmission, especially as countries continue to reopen despite surges in cases.

“We hope that our statement will raise awareness that airborne transmission of COVID-19 is a real risk and that control measures, as outlined above, must be added to the other precautions taken, to reduce the severity of the pandemic and save lives,” the group said.