According to the Federal Office of Public Health (FOPH), aerosols dissipate quickly in the open air, so the risk of contamination is low, especially if walking past an infected person without any contact or interaction.
However, authorities said masks must be worn outdoors if “the concentration of people does not allow the necessary distances to be respected”.
Face protection is already required in many other places across Europe.
Epidemiologist Marcel Tanner, who is a member of Switzerland’s Covid-19 Task Force, said that due to the alarming increase in the number of infections, hospitalisations and deaths that Switzerland has experienced in the past three weeks, expanding the mask requirement to outdoor spaces “makes sense”, as infection can sometimes occur in open air.
The measure is particularly important on busy and crowded streets where the 1.5-metre distance rule cannot be respected, he added.
“It’s true that nothing works 100 percent. But if you wear a mask outdoors in addition to following hygiene and distancing measures, you will cut your risk of contamination significantly,” he said.
Bruno Grandbastien, a doctor in the infection prevention unit of the University Hospital in Lausanne (CHUV), said in an interview with RTS public broadcaster that the measure “is based more on common sense than on scientific studies”.
“Masks do serve a purpose in outdoor spaces, especially when people are in close proximity to each other during pandemics,” he said. “In such situations, infections have been known to happen”.
On the other hand “masks should not be imposed when people walk alone in the forest or the mountains”, as there is no risk of catching Covid in large and empty spaces, he added.