NEW YORK • The World Health Organisation (WHO) has acknowledged "emerging evidence" of airborne transmission of the coronavirus, which an international group of scientists found can stay aloft for hours in tiny droplets in stagnant air and infect people as they inhale.
This risk is highest in crowded indoor spaces with poor ventilation and may help explain super-spreading events reported in meatpacking plants, churches and restaurants.
The WHO said it would put out a new scientific brief within days, after the group of 239 scientists concluded the virus could travel far beyond 2m.
The scientists said exhaled droplets under 5 micrometers in size that contain the virus can suspend in the air for several hours and travel up to tens of metres.
The 2m physical distancing guideline has been a major element in the fight against Covid-19, which has killed more than 547,000 people and infected 12 million since it emerged in China last December.
Dr Benedetta Allegranzi, the WHO's technical lead on infection control, said at a virtual press conference: "We acknowledge that there is emerging evidence in this field.
"We believe that we have to be open to this evidence and understand its implications regarding the modes of transmission and also regarding the precautions that need to be taken."
In a letter, the group of scientists had called on the WHO to recommend that people avoid overcrowding, particularly on public transportation and in other confined spaces.
Public buildings, businesses, schools, hospitals and care homes should also supply clean air, minimise recirculating air and consider adding air filters and virus-killing ultraviolet lights, they said.
"Public health agencies around the world take their cues from WHO and, hopefully, this will lead to greater emphasis on wearing of face coverings and avoiding the three Cs: close contact, closed and poorly ventilated spaces and crowds," said Dr Linsey Marr, an aerosol expert at Virginia Tech in the United States.
Meanwhile, WHO directorgeneral Tedros Adhanom Ghebreyesus said the pandemic was showing no signs of slowing down, after 400,000 new cases were reported over the weekend. It took 12 weeks for the world to reach the first 400,000 Covid-19 cases.
"The outbreak is accelerating and we've clearly not reached the peak of the pandemic," Dr Tedros said.
"While the number of deaths appears to have levelled off globally, in reality some countries have made significant progress in reducing the number of deaths, while in other countries, deaths are still on the rise."
The WHO is sending an animal health expert and an epidemiologist to China this weekend to lay the groundwork for an investigation into the animal origins of the virus. Dr Tedros said they would develop the scope and terms of reference for a WHO-led international mission that would pick up from the work already undertaken in China.
The US confirmed on Tuesday that it will leave the WHO on July 6 next year. US President Donald Trump has accused the agency of becoming a puppet for China during the Covid-19 pandemic. The WHO denies this.
But Mr Joe Biden, the presumptive Democratic presidential nominee, said he would rejoin the WHO immediately if he wins.
"Americans are safer when America is engaged in strengthening global health. On my first day as President, I will rejoin the @WHO and restore our leadership on the world stage," the former vicepresident tweeted.
NYTIMES, REUTERS, AGENCE FRANCE-PRESSE