After a bumpy start in the coronavirus response, Ursula von der Leyen, the president of the European Commission, secured a major win in June, placing the bureaucracy she leads at the heart of the European Union’s pandemic response. She was entrusted with cutting deals with pharmaceutical companies to provide vaccines for the 450 million people in the bloc.
When the rollout finally started just after Christmas, a sense of relief took hold in Brussels: The work of the commission, the European Union’s executive branch, was largely done; now individual member states were in charge of putting vaccines in the arms of citizens.
But barely a month into the rollout, which was shaping up to be significantly behind Britain and the United States, Pfizer and then AstraZeneca informed the commission that they would not deliver doses as promised, mainly because of production problems.
While the issue with Pfizer appeared limited and manageable, the situation with AstraZeneca escalated into an all-out vaccine war between the European Union and Britain. The company had been smoothly delivering vaccines to Britain, just as it informed the bloc that it would slash 75 percent off its promised first-quarter delivery volumes.
By the middle of last week, Ms. von der Leyen, who had not made any public statements on the matter, had left her health commissioner, Stella Kyriakides of Cyprus, to face the news media.
Later in the week, the commission rolled out a half-baked policy requiring prior authorization for exports of vaccines made in the European Union, so that it could check that companies like Pfizer and AstraZeneca were not sending overseas any vaccines that had been promised to the bloc.
Critics accused the European Union, which spent years criticizing the Trump administration for erecting trade barriers, of doing the same. And Brexit supporters accused the bloc of trying to take vaccines away from Britons.
The idea came from Ms. von der Leyen and her inner circle, several senior E.U. officials said.
On Friday night, as the legal text of the policy was published, reporters noticed it made provisions for the European Union to activate a nuclear clause in the divorce terms with Britain, known as Article 16 of the Northern Ireland Protocol, which practically reinstitutes a hard border on the island of Ireland.
The idea was that activating that clause would close a loophole that could allow Britain to spirit vaccines away from the E.U. by using the lack of border between the Republic of Ireland, an E.U. country, and Northern Ireland, which is part of the United Kingdom.
The fallout was fast and furious. By 1 a.m. Saturday, after several tense calls, including with Prime Minister Boris Johnson of Britain, Ms. von der Leyen reversed the Article 16 invocation.