For many members of this globe-spanning flock, the annual celebration is the high point 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.