From the stage of an evangelical superchurch, the leader of the gospel choir kicked off an evening of prayer and preaching: "We're going to celebrate the Lord! Are you feeling the joy tonight?"
"Yes!" shouted the hundreds gathered at the Christian Open Door church on February 18. Some of them had travelled thousands of miles to take part in the week-long gathering in Mulhouse, a city of 100,000 on France's borders with Germany and Switzerland.
For many members of this globe-spanning flock, the annual celebration is the highpoint of the church calendar. This time, someone in the congregation was carrying the coronavirus.
The prayer meeting kicked off the biggest cluster of Covid-19 in France - one of northern Europe's hardest-hit countries - to date, local government said. Around 2,500 confirmed cases have been linked to it.
Worshippers at the church have unwittingly taken the disease caused by the virus home to the West African state of Burkina Faso, to the Mediterranean island of Corsica, to Guyana in Latin America, to Switzerland, to a French nuclear power plant, and into the workshops of one of Europe's biggest automakers.
Weeks later, Germany partially closed its border with France, suspending a free-movement pact that has been in place for the past 25 years.
The church cluster was a key factor, two people familiar with the German decision told Reuters. Church officials told Reuters that 17 members of the congregation have since died of complications linked to the disease.
Other religious gatherings have been linked to the spread of the virus: A large church in South Korea has triggered more than 5,000 cases there.