A man receives his first dose of the Pfizer coronavirus vaccine in Elmont, N.Y., on April 14. (Mary Altaffer/AFP/Getty Images)

The United States is on track to have gathered an oversupply of hundreds of millions of coronavirus vaccine doses as soon as July, even while many countries in the developing world will have to wait years to vaccinate a majority of their populations, according to a report by the Duke Global Health Innovation Center.

The estimates, included in the paper alongside recommendations, come as the Biden administration faces mounting pressure to facilitate equitable vaccine distribution around the world. The United States has pledged money to the global immunization effort, but has resisted calls to share vaccine technology or donate surplus doses.

On Thursday, Secretary of State Antony Blinken held a fundraising event for Covax, a World Health Organization-backed push to distribute coronavirus vaccines, particularly to low- and middle-income countries, and called on other nations to do more.

Covax aims to secure and distribute enough vaccine to reach up to 20 percent of the population in 92 participating target countries by the end of 2021. In February, the Biden White House pledged up to $4 billion in support, reversing a Trump administration decision to opt out.

At a virtual event on Thursday, Blinken urged countries to give more, saying an additional $2 billion could help Covax reach 30 percent, rather than 20 percent, of target populations this year. “Just think for a moment of all the people whose lives would be impacted by hitting that higher target.” he said.

The secretary of state said countries must support vaccine manufacturing, but stopped short of announcing any specific policies or plans. He did not address the issue of surplus U.S. doses.

On Wednesday, Oxfam released a letter signed by more than 100 former heads of state and Nobel laureates calling on President Biden to waive intellectual property rules for coronavirus vaccines and “put the collective right to safety for all ahead of the commercial monopolies of the few.”

“Leadership from the US on safe, effective, and equitable global access to Covid-19 vaccines is imperative,” the Duke paper argues, pushing for Washington to increase funding for vaccine-sharing programs and to donate excess doses and use its clout to open up vaccine manufacturing.

Another proposal, put forward in a letter backed by the Center for Strategic and International Studies (CSIS), calls for the United States to donate 10 percent of its excess doses over the summer, moving to 50 percent by the end of the year, and argues that Biden should deliver a speech this spring to make the case to the American people.

Biden faces pressure to distribute vaccines worldwide, while Americans still need them at home

Under the leadership of Gayle Smith, Blinken’s new coordinator for global coronavirus response and health security, the ONE Campaign, a nonprofit organization, called on wealthy countries to donate 5 percent of their surplus doses once they’ve vaccinated 20 percent of their populations.

The proposals come just after the United States surpassed that 20 percent target — and as the virus spreads uncontrolled in much of the world and more-virulent variants continue to take hold.

The United States will probably have “at least 300 million excess doses or more” by the end of July, the Duke paper’s authors estimate, even as vaccination programs are extended to the vast majority of U.S. children.

The estimate is based on the assumption that the vaccine developed by AstraZeneca receives emergency-use authorization and the Johnson & Johnson vaccine is used widely, despite rare side effects.

CDC Director Rochelle Walensky on April 14 detailed why there was a call for pause in the use of the Johnson & Johnson vaccine. (Video: The Washington Post)

The zero-sum vaccine game: How a dose in the U.S. takes a dose away from a poorer country

The oversupply in the United States forms a stark contrast with the situation in many poorer parts of the world, where vaccination programs have been slow to begin amid problems with supply and distribution, and could ultimately prolong the pandemic and hamper a U.S. recovery.

The Biden administration has pledged to donate doses. “If we have a surplus, we’re going to share it with the rest of the world,” Biden said last month, when pressed on the issue. “We’re going to start off making sure Americans are taken care of first, but we’re then going to try to help the rest of the world.” Blinken has made the case that protecting Americans requires international action. “This pandemic won’t end at home until it ends worldwide,” he said at a news conference on April 5. But no global plan to donate doses has been specified.

The world’s poorest 92 countries will not be able to reach a vaccination rate of 60 percent of their populations until 2023 “or beyond” if current distribution trends continue, the Duke paper estimates.

The authors include former U.S. officials such as Mark McClellan, who served as commissioner of the Food and Drug Administration under President George W. Bush, as well as Krishna Udayakumar, founding director of the Duke Global Health Innovation Center.

Their recommendations echo the concerns from other public health experts worldwide, including World Health Organization Director General Tedros Adhanom Ghebreyesus, who called vaccine-distribution plans that focus only on domestic issues a “self-defeating strategy [that] will cost lives and livelihoods.”

French President Emmanuel Macron in February pushed for the United States and Europe to donate up to 5 percent of secured vaccine doses, although the idea has not gained significant momentum.

Covax is just one part of the broader Access to COVID-19 Tools (ACT) Accelerator, a broader plan that has a funding gap of more than $22 billion.

Even if Covax were fully funded this year, it would be able to vaccinate only a quarter of the populations in the world’s 92 poorest nations, according to the Duke paper.

Drug companies defend vaccine monopolies in face of global outcry

Although many experts say the United States needs to do more to ensure the developing world can vaccinate faster, they differ on approach.

While the letter spearheaded by Oxfam called on the United States to back a temporary waiver of World Trade Organization intellectual property rules, breaking vaccine monopolies, the Duke experts argued that such a measure is unnecessary and could prove chaotic.

Instead, they propose that the United States should back the use of cooperative licensing arrangements to increase manufacturing capacity, so that production can be scaled up quickly but safely.

The Duke authors also state that although U.S. contracts with drug manufacturers may restrict donations of excess doses, the Biden administration could modify its contracts and could provide “loans” of currently available vaccine doses (as it has done with Mexico and Canada). It also could shift the timing of vaccine deliveries so more-needy countries receive their doses first.

Both the Duke and CSIS proposals noted that although the AstraZeneca vaccine does not have emergency-use approval in the United States, it could be used in other countries. The United States has purchased 300 million doses of the AstraZeneca vaccine alone.

This report has been updated.

Read more:

Vaccination rates are rising, but so are covid cases

Nearly 20 percent of the U.S. population is fully vaccinated. Many countries may not hit that target this year.

Yellen warns that slow vaccine rollout in poor countries poses threat to U.S.

Coronavirus: What you need to know

Covid isolation guidelines: Americans who test positive for the coronavirus no longer need to routinely stay home from work and school for five days under new guidance planned by the Centers for Disease Control and Prevention. The change has raised concerns among medically vulnerable people.

New coronavirus variant: The United States is in the throes of another covid-19 uptick and coronavirus samples detected in wastewater suggests infections could be as rampant as they were last winter. JN.1, the new dominant variant, appears to be especially adept at infecting those who have been vaccinated or previously infected. Here’s how this covid surge compares with earlier spikes.

Latest coronavirus booster: The CDC recommends that anyone 6 months or older gets an updated coronavirus shot, but the vaccine rollout has seen some hiccups, especially for children. Here’s what you need to know about the latest coronavirus vaccines, including when you should get it.