People living in areas with where COVID-19 is spreading should always wear masks in shops, workplaces and schools that lack adequate ventilation, the World Health Organisation (WHO) said on Wednesday.
If they cannot maintain physical distancing of at least one metre (3 ft), people in those indoor locations - including children and students aged 12 or over - should also wear a mask even if the spaces are well ventilated, it said in a tightening of its guidelines, reports Reuters.
They should also wear masks outdoors if physical distancing cannot be maintained, it said.
WHO spokeswoman Margaret Harris said the recommendations were among the biggest changes to its guidance on mask-wearing, and updated advice from June.
"If indoors, unless ventilation has been assessed to be adequate, WHO advises that the general public should wear a non-medical mask, regardless of whether physical distancing of at least 1 metre can be maintained," the WHO said.
It also advised "universal masking" in all health care facilities including in common areas such as cafeterias and staff rooms.
Health workers could wear N95 masks if available when caring for COVID-19 patients, but the only proven protection is when they are doing aerosol-generating procedures, the WHO said.
