Matt Apuzzo and Selam Gebrekidan

BRUSSELS — The calls began in December, as the United States prepared to administer its first batches of Covid19 vaccine. Even then, it was clear that the European Union was a few weeks behind, and its leaders wanted to know what they could learn from their American counterparts.

The questions were the same, from President Emmanuel Macron of France, President Ursula von der Leyen of the European Commission, and Alexander De Croo, the prime minister of Belgium.

“How did you do it?” Dr. Moncef Slaoui, the United States vaccine czar, recalled them asking on the calls. “And what do you think we missed?”

Since then, the rollout gap between Europe and the U.S. has only widened, and some of the countries hardest hit early in the pandemic are facing a deadly third wave of infections. France, large parts of Italy, and other regions are back in lockdown. Roughly 20,000 Europeans die of COVID-19 each week.

The Continent was dealt a further setback when a scare over blood clots and brain bleeds led several countries last week to temporarily halt the distribution of the AstraZeneca vaccine. Most of them resumed using it on Friday, after Europe’s top drug regulator vouched for its safety, but public confidence in the shot has been badly shaken.

Vaccine salvation remains, for now, still tantalizingly out of reach. Only about 10% of Europeans have received a first dose, compared with 23% in the United States and 39% in Britain.

There is no single culprit. Rather, a cascade of small

Countries across Europe resumed vaccinations with the AstraZeneca shot on Friday, as leaders sought to reassure their populations it is safe following brief suspensions that cast doubt on the vaccine.

decisions have led to increasingly long delays. The bloc was comparatively slow to negotiate contracts with drugmakers. Its regulators were cautious and deliberative in approving some vaccines. Europe also bet on vaccines that did not pan out or had supply disruptions. And national governments snarled local efforts in red tape.

But the biggest explanation, the one that has haunted the bloc for months, is as much philosophical as it was operational. European governments are often seen in the U.S. as free-spending, liberal bastions, but this time it was Washington that threw billions at drugmakers.

In short, the answer today is the same as it was in December, said Dr. Slaoui. The bloc shopped for vaccines like a customer. The U.S.basically went into business with the drugmakers, spending much more heavily to accelerate vaccine development, testing and production.

“They assumed that simply contracting to acquire doses would be enough,” recalled Dr. Slaoui, whom

President Donald J. Trump hired to speed the vaccine development. “In fact what was very important was to be a full, active partner in the development and the manufacturing of the vaccine. And to do so very early.”

The result in Europe is a stumbling inoculation effort that has led to political fallout, with leaders pointing fingers over why some of the world’s richest countries, home to factories that churn out vast quantities of vaccine, cannot keep pace with other wealthy nations in injecting its people.

Compared with nearly all the rest of the world, the European Union is in an admirable position. Its leaders say it remains feasible to vaccinate 70% of the Continent by this summer. The bloc has ordered enough doses to fully vaccinate its population at least three times, to the consternation of countries that will wait years for full coverage.

But Europeans are stung, especially, to see Britain’s rollout going so well after the country exited the bloc.

Denmark on Saturday reported that two people had experienced brain hemorrhages after receiving the AstraZeneca Covid vaccine, one of whom died. The Danish Medicines Agency said it was looking into whether the condition was a potential side effect.

A spokesperson for the Capital Region of Denmark confirmed the death, and the Danish Ritzau news agency reported that the other person, a female civil servant in her 30s, was critically ill.

Millions in dozens of countries have received the AstraZeneca Covid vaccine with few reports of ill effects. After several countries recently paused the use of the vaccine, the European Medicines Agency reviewed and said that it considered the vaccine safe, although it would continue to watch for any connections to blood disorders. The agency noted that any threat would be very small, and that the shots will prevent vastly more deaths than they might cause.

Recent blood clots and abnormal bleeding in a small number of vaccine recipients in European countries raised questions about its safety, and prompted the suspensions. That created a disruptive pause in vaccination campaigns this week, even as some European countries were entering a third wave of infections.

“Right now we are examining whether this is the exact same disease picture with multiple blood clots, a low count of platelets and hemorrhages,” said Tanja Erichsen, a director at the Danish Medicines Agency.

“We prioritize reports of suspected serious side effects such as these and examine them thoroughly to assess whether there is a possible link to the vaccine,” Erichsen said in a tweet on Saturday. “We are in the process of dealing with the two specific cases.”

This is the second death in Denmark after a person was given the AstraZeneca vaccine.