The World Health Organisation is acknowledging the possibility that COVID-19 might be spread in the air under certain conditions - after more than 200 scientists urged the agency to do so.
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In an open letter published this week in a journal, two scientists from Australia and the US wrote that studies have shown "beyond any reasonable doubt that viruses are released during exhalation, talking and coughing in microdroplets small enough to remain aloft in the air".
The researchers, along with more than 200 others, appealed for authorities including the WHO to adopt more stringent protective measures.
WHO has long dismissed the possibility that the coronavirus is spread in the air except for certain risky medical procedures, such as when patients are first put on breathing machines.
In a change to its previous thinking, WHO noted on Thursday that studies evaluating COVID-19 outbreaks in restaurants, choir practices and fitness classes suggested the virus might have been spread in the air.
Airborne spread "particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out," the organisation said.
Still, officials also pointed out that other modes of transmission - like contaminated surfaces or close contacts between people in such indoor environments - might also have explained the disease's spread.
WHO's stance also recognised the importance of people spreading COVID-19 without symptoms, a phenomenon the organisation has long downplayed.
WHO has repeatedly said such transmission is "rare" despite a growing consensus among scientists globally that asymptomatic spread likely accounts for a significant amount of transmission.
The agency said that most spread is via droplets from infected people who cough or sneeze, but added that people without symptoms are also capable of transmitting the disease.
"The extent of truly asymptomatic infection in the community remains unknown," WHO said.
It comes as health authorities, officials and businesses urged the use of face coverings around the world.
Spain's Balearic Islands will make wearing face masks in public compulsory at all times from Monday, joining Catalonia in going further than a central government directive that mandates their use only when in close proximity to others.
Catalonia's order began on Thursday just as tourists were starting to return after coronavirus lockdowns and travel restrictions lifted.
In Belgium, the government's health advisers have recommended wearing masks in shops to keep the spread of the coronavirus at its current low level.
The health ministry's scientific advisory body said face masks play a crucial role in limiting the diffusion of droplets of respiratory secretions potentially carrying the deadly virus.
Among the measures adopted to fight the virus, the Belgian government has made the use of masks compulsory on public transportation but customers still have the option to run errands without any protection.
The health superior council said it recommends masks in shops because physical distancing is difficult in stores.
Coffee chain Starbucks said on Thursday it will require customers to wear masks at all of its cafes in the United States.
The company said that customers who are not covering their faces will still be able to order at drive-throughs or delivery.
Starbucks said the move, which comes into effect on July 15, was part of an "effort in prioritising the health and well-being of partners (employees) and customers".
Australian Associated Press
