President Biden is set to take the global stage this week with a coronavirus vaccine-sharing strategy that has been panned by congressional Democrats and some health advocates as too timid, drawn flak from European allies as too bold and led to frustration within his administration.

It has also prompted a flurry of White House efforts to answer critics, with new announcements to bolster the plan expected ahead of the president’s appearance at the Group of Seven summit in Britain this weekend.

The United States is “working with our G-7 partners on a larger effort to help end the pandemic so that the world’s democracies deliver for people everywhere. And we will have more to say about this” at the meeting, Jake Sullivan, Biden’s national security adviser, told reporters Thursday. The White House has been exploring ways to boost global vaccine supply, and people familiar with the plans say an announcement could be made as soon as this week.

The summit — Biden’s first international trip as president — poses multiple diplomatic challenges for a White House seeking to restore the United States’ international luster amid a pandemic that has rattled the globe and left wealthy nations struggling to meet the scale of the crisis.

Even as the outbreak recedes in the United States, infections have surged in developing countries that lack shots, prompting some public health experts and officials to charge that rich nations have hoarded doses and fostered “vaccine apartheid.” Fewer than 2 percent of people in Africa have received at least one dose of a coronavirus vaccine, compared with more than 50 percent in the United States and United Kingdom.

But Biden, like virtually every political leader, faced a delicate balancing act addressing the need to vaccinate the world while pushing to get his own country immunized.

Meanwhile, Biden’s surprise push to temporarily waive patent protections for coronavirus vaccines to bolster production in the developing world created new tensions with the European Union, which criticized the idea as wrongheaded and inadequate because it would not boost vaccine production for months or even years. The E.U. last week offered a counterproposal that would preserve drug companies’ intellectual property in most cases, setting up a showdown with the United States.

Biden also is seeking to renew alliances damaged by President Donald Trump, with health experts lamenting that opportunities to address the global crisis were lost amid his predecessor’s clashes with the World Health Organization. And some health, diplomatic and global aid experts inside the Biden administration continue to voice frustrations that the U.S. strategy remains piecemeal compared with more-comprehensive proposals from global aid groups.

As the G-7 nations prepare to meet, more than 200 prominent figures — including more than 100 former government leaders — this week called for them to spend $44 billion to help vaccinate low-income countries.

“It’s time to make a big decision,” said Gordon Brown, the former United Kingdom prime minister, who called on the group’s wealthy member nations to agree on a global financing plan, citing a death toll that often tops 10,000 per day. “It would be a catastrophic, unforgivable moral failure if we did not have a plan to vaccinate the world this weekend.”

Biden also is facing pressure from congressional Democrats, who have praised the president’s commitment to share 80 million doses this month but have warned that rivals such as China and Russia have used vaccine deals with dozens of countries to advance their own interests.

Four Democrats introduced legislation Tuesday that aims to help vaccinate at least 60 percent of the people living in countries eligible to receive vaccine through Covax, the WHO’s initiative to distribute vaccine. The $34 billion proposal would create a new program to coordinate the U.S. pandemic response, modeled on the global HIV/AIDS program begun under the George W. Bush administration, according to legislative text shared with The Washington Post.

“So long as covid-19 continues to thrive anywhere, it’s a threat to everyone everywhere,” said Rep. Raja Krishnamoorthi (D-Ill.), who introduced the bill with Rep. Pramila Jayapal (D-Wash.), who chairs the Congressional Progressive Caucus, and Sens. Elizabeth Warren (D-Mass.) and Jeff Merkley (D-Ore.).

The White House has acknowledged its current response is insufficient to end the pandemic, with Sullivan and other officials saying they are pursuing plans to donate more U.S. doses, help boost global manufacturing capacity and take other steps to lead the world’s coronavirus response.

The administration also has countered with a flurry of diplomatic activity ahead of the summit, with Biden last week outlining his initial plan to share 25 million doses globally and the State Department on Tuesday easing travel warnings for dozens of nations amid demands from allies.

U.S. officials say they are pivoting after prioritizing a domestic response that has vaccinated more than half of Americans and led cases to plunge.

“The U.S. is headed into the G-7 in a position of strength,” Jeff Zients, the White House coronavirus coordinator, said in a statement. “The President will use this momentum to rally the world’s democracies around solving this crisis globally, with America leading the way to create the arsenal of vaccines that will be critical in our global fight against covid-19.”

G-7 officials have grown increasingly vocal on the vaccine-sharing issue, promising bold action, but without putting forward detailed plans. British Prime Minister Boris Johnson said over the weekend that he would urge his counterparts to “rise to the greatest challenge of the post-war era” and vaccinate “the world by the end of next year” — without mentioning precisely how.

With the gap between vaccine “haves” and “have-nots” widening, the world wants and needs them to deliver big, said J. Stephen Morrison, director of the Global Health Policy Center at the Center for Strategic and International Studies.

“The argument is being won at a conceptual level,” Morrison said. “But beyond winning the argument and having a conceptual agreement is the question, ‘Who does what?’”

Days before the summit, all that still seemed up in the air.

“The G-7 is on the spot because these are the countries that have surplus vaccine,” said Mara Pillinger, a senior associate in global health policy and governance at Georgetown University’s O’Neill Institute for National and Global Health Law.

However, it is not clear the group shares a common vision for what to do next. Part of the problem is that members are at different stages of their own vaccination efforts. Roughly 62 percent of Canada’s population, 60 percent of the U.K. population and 51 percent of the U.S. population have had at least one dose of vaccine, according to estimates from Our World in Data. Germany, Italy and France are all between 40 and 45 percent of residents receiving one dose. In Japan, about 11 percent of people have had a dose.

Global public health experts have rattled off wish lists, with John Nkengasong, director of the Africa Centers for Disease Control and Prevention, asking for two specific commitments.

“One is to redistribute those excess doses of vaccines that are out there immediately, so that we can put it in the hands of people in Africa,” he said, citing the continent’s lagging vaccination rates. “And second is to work with Africa and other parts of the world to begin to decentralize and regionalize our ability to manufacture … vaccines, diagnostics and therapeutics.”

Nkengasong also echoed a call from other experts who appealed to the G-7 to set up a new coordinated organization akin to the Global Fund to Fight AIDS, Tuberculosis and Malaria, which the wealthy nations helped create nearly two decades ago to combat HIV/AIDS around the world.

“This is the most severe crisis of our time,” Nkengasong added. “And history will remember us if we do the right things and do it quickly.”

Brown, the former U.K. prime minister, shared that assessment, saying he hoped the United States would step forward “as it always has in critical, decisive moments.”

“This is a turning point,” Brown said. “We’re going to prove in the next few months whether international cooperation is going to work or whether it’s inadequate and insufficient.”

Tyler Pager in Washington and Karla Adam in London contributed to this report.