At the late September yodelling event in the rural Schwyz canton, people in the audience were asked to maintain social distancing, but mask-wearing was not required.
“We can’t do anything about what happened with this yodelling group. We found out nine days after the performances that several people from the group were infected,” event organiser Beat Hegner told RTS public television.
Now the pandemic has spread through the region, with 1,238 cases compared with just 500 in mid-September.
On Wednesday alone, 94 people tested positive, twice as many as the day before.