In a memo, published in English on its website, the Norwegian Institute of Public Health, said that even in the best case, with medical masks which prevent 40 percent of infections, 200,000 people would have to wear them to prevent just one new infection per week.
This, it said, meant that the likely negative impacts outweighed any benefits “in the current epidemiological situation”.
“The number of people who experience undesirable effects is likely to be much larger than the number of infections prevented,” it said.
It said, however, that the authorities should look again at face masks if the pandemic flares up again.
“If epidemiological situation worsens substantially in a geographical area, the use of face masks as a precautionary measure should be reconsidered,” it said.
“Measures to reduce risks during necessary public transport and during mass events, including wearing face masks, should be explored further.”
In the memo, described as a “rapid review of the evidence”, the institute acknowledged that the World Health Organisation had updated its guidelines, and now recommended countries ask citizens to wear masks in “settings where individuals are unable to keep a physical distance of at least 1 metre.”
“There is evidence of a protective effect of medical face masks against respiratory infections in community settings,” the institute conceded. “However, study results vary greatly.”
It noted, however, that “countrywide training programmes” would be needed to stop incorrect use of medical face masks.
In addition, it said it was likely many people would use non-medical face masks whose effectiveness has not yet been adequately demonstrated.
Many people find masks uncomfortable, and experience problems breathing and communicating, it argued. There was also a risk that masks would generate a false sense of security, leading to people to drop other protective measures.