Of all the things that are still unknown about the novel coronavirus, it’s mode of transmission isn’t one of them. Or at least, that’s what we think! Earlier this week, a group of over 200 scientists sent an open letter to the World Health Organisation, presenting compelling evidence of how SARS-CoV-2 (the virus that causes covid-19) is also airborne—urging the international health agency to revise its recommendations.
Now, the WHO is openly acknowledging the emerging evidence of the airborne spread of the novel coronavirus. “We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of covid-19,” said Maria Van Kerkhove, technical lead on the covid-19 pandemic at the WHO.
How does covid-19 spread?
The WHO has previously said the virus that causes the covid-19 respiratory disease spreads primarily through small droplets expelled from the nose and mouth of an infected person that quickly sink to the ground.
So a person can only get infected when you’re close to an infected person and have inhaled these droplets. The covid-19 virus can also stay on different surfaces for a long time, though according to scientific data the chances of person-to-person transmission are much higher than surface-to-person transmission.
However, in the open letter which was published in the Clinical Infectious Diseases journal, 239 scientists in 32 countries outlined evidence that they say shows floating virus particles can infect people who breathe them in. Because those smaller exhaled particles can linger in the air, the scientists in the group had been urging WHO to update its guidance.
“We wanted them to acknowledge the evidence,” said Jose Jimenez, a chemist at the University of Colorado who signed the paper.
However, Benedetta Allegranzi—WHO’s technical lead for infection prevention and control—said at a press briefing that the evidence was not definitive.
“…The possibility of airborne transmission in public settings – especially in very specific conditions, crowded, closed, poorly ventilated settings that have been described, cannot be ruled out,” she said.
“However, the evidence needs to be gathered and interpreted, and we continue to support this.”
Jimenez said historically, there has been fierce opposition in the medical profession to the notion of aerosol transmission, and the bar for proof has been set very high. A key concern has been a fear of panic.
“If people hear airborne, healthcare workers will refuse to go to the hospital,” he said. Or people will buy up all the highly protective N95 respirator masks, “and there will be none left for developing countries.”
What will happen if the WHO changes its guidelines?
Any change in the WHO’s assessment of the risk of transmission could affect its current advice on keeping 1-metre (3.3 feet) of physical distancing. Governments, which rely on the agency for guidance policy, may also have to adjust public health measures aimed at curbing the spread of the virus.
Van Kerkhove said the WHO would publish a scientific brief summarising the state of knowledge on modes of transmission of the virus in the coming days.
“A comprehensive package of interventions is required to be able to stop transmission,” she said.
“This includes not only physical distancing, it includes the use of masks where appropriate in certain settings, specifically where you can’t do physical distancing and especially for healthcare workers.”