The coronavirus upset a summit of European Union leaders in Brussels on Thursday as one of the key participants, EU Commission chief Ursula von der Leyen, had to quit the meeting minutes after it began to go into precautionary self-isolation.

Planned meetings of the 27 EU nations’ leaders have been disrupted by the coronavirus pandemic since the spring. Some have been postponed and some held by video-conference, but they returned to in-person summits over the summer as infection rates eased.

On Thursday, for the first time, they faced a potential threat in the very room where they were meeting, when von der Leyen told them she had been in contact with an infected person.

“I have just been informed that a member of my front office has tested positive for COVID-19 this morning,” the president of the bloc’s executive tweeted minutes into the meeting.

“As a precaution, I am immediately leaving the European Council to go into self-isolation,” she said, adding that she herself had tested negative for the virus.

Under Belgian rules, she is now required to self-isolate for seven days. The summit continued after her departure, a spokesman for the European Council said.

A European diplomat said the summit was unlikely to be disrupted as leaders kept at safe distance from each other.

The two-day meeting was called to discuss Brexit and climate change, but a debate on the pandemic was added to the agenda after a second spike of infections across Europe.

Von der Leyen, 62, was supposed to brief leaders on Friday about European Commission-led negotiations with pharmaceutical companies to secure potential COVID-19 vaccines.

A physician by training, von der Leyen was forced into quarantine last week after she had contact with another infected person.

Minutes before going back into quarantine on Thursday, she had urged leaders to agree on common rules for the length of self-isolation. EU governments began diverging over the last weeks from the global standard of a 14-day period, with many of them shortening it.

In September the head of the European Council and chairman of EU summits, Charles Michel, had to postpone a leaders’ meeting for a week after going into quarantine.

EU leaders usually meet in Brussels at least four times a year to set the bloc’s political agenda. It is not yet clear if the resurgence of coronavirus infections will send them back to video-conferencing when they meet again in December.

REUTERS