Hundreds of scientists say there is evidence that novel coronavirus is airborne, meaning virus particles can hover in the air and infect people.
As a result, they are are calling for the World Health Organisation [WHO] to revise its recommendations, the New York Times reports.
The experts believe fresh cases of the killer bug – in particular in worrying clusters – indicate the virus lingers in the air indoors, infecting those nearby.
It comes as England re-opened pubs for the first time in three months on Saturday with photos and video showing large crowds failing to adhere to social distancing rules.
The WHO has said the coronavirus disease spreads primarily from person to person through small droplets from the nose or mouth, which are expelled when a person with COVID-19 coughs, sneezes or speaks.
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In an open letter to the agency, which the researchers plan to publish in a scientific journal next week, 239 scientists in 32 countries outlined the evidence showing smaller particles can infect people, the NYT said.
Whether carried by large droplets that zoom through the air after a sneeze, or by much smaller exhaled droplets that may glide the length of a room, the coronavirus is borne through air and can infect people when inhaled, the scientists said, according to the NYT.
However, the health agency said the evidence for the virus being airborne was not convincing, the newspaper added.
“Especially in the last couple of months, we have been stating several times that we consider airborne transmission as possible but certainly not supported by solid or even clear evidence,” Dr Benedetta Allegranzi, the WHO’s technical lead of infection prevention and control, said.
However, Dr Trish Greenhalgh, a primary care doctor at the University of Oxford warned: “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.
“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,” she said. “So why not just mask up for a few weeks, just in case?”
It comes as cases of Covid-19 continued to surge over the weekend.
The WHO reported more than 200,000 new cases globally of the disease for the first time in many places on Saturday.
At the same time, life is returning to normal in many places.
In light of pubs and restaurants re-opening throughout England over the weekend, Police Federation National Chair John Apter said it was “crystal clear” that drunk people were unable to practice social distancing.
But Britain’s health minister Matt Hancock said on Sunday people in England had largely behaved themselves after the latest step towards a return to normality from the coronavirus lockdown.