More than 175 public health experts, scientists and activists on Tuesday demanded that President Biden take urgent steps to confront the global spread of the coronavirus, warning that without immediate action to inoculate the rest of the world, newer variants are likely to emerge — including ones that may evade vaccines’ protection.

“We urge you to act now,” the experts wrote in a joint letter to senior White House officials Tuesday and shared with The Washington Post. “Announcing within the next 30 days an ambitious global vaccine manufacturing program is the only way to control this pandemic, protect the precious gains made to date, and build vaccine infrastructure for the future.”

The health experts also address Biden directly in a separate letter, underscoring that the delta variant is causing a surge of infections across the globe, including in Africa, Latin America and Asia, where many residents have yet to receive a single dose. Meanwhile, they note, the United States has stockpiled more than 55 million doses of mRNA vaccines but is administering fewer than 900,000 per day, with millions of Americans still balking at getting the shots.

Johns Hopkins University epidemiologist Gypsyamber D'Souza explains how the U.S. can reach coronavirus herd immunity and what happens if that goal is missed. (Brian Monroe, John Farrell/The Washington Post)

“At this rate, it would take over two months to administer just the vaccine doses currently stored,” wrote the authors, urging Biden to begin distributing millions of stockpiled doses per week.

The letters’ co-signers include Tom Frieden, who led the Centers for Disease Control and Prevention during the Obama administration; Linda Fried, the dean of Columbia University’s public health school; Paul Farmer, the co-founder of Partners in Health, a nonprofit group focused on the developing world; and other leaders in global health and infectious disease. More than 50 organizations also co-signed the letter.

The White House did not immediately respond to a request for comment.

Several signers said they have privately appealed to senior Biden administration officials, including infectious-disease expert Anthony S. Fauci and top pandemic adviser David Kessler, but had grown frustrated with the slow pace of movement on global vaccinations. Fewer than 4 percent of Africans and about 30 percent of Asians have received at least one dose of a coronavirus vaccine, compared with nearly 60 percent of Americans, according to the University of Oxford’s Our World in Data project.

The White House has been criticized for months by public health experts who say Biden has announced piecemeal steps to confront the global crisis but done too little to ramp up immediate vaccine production.

“We’ve been pushing Fauci and Kessler hard on this for months, and they, in turn, have been pushing those above them. But the world has nothing to show for it,” said Peter Staley, a co-founder of PrEP4All Collaboration, an HIV/AIDS advocacy organization that has pivoted to coronavirus activism.

Staley and other letter-signers vowed increasingly intense protests, including targeting officials and companies that are perceived to be delaying the response. “Pharma took years before letting the rest of the world access their AIDS drugs,” he said. “We won’t let that happen with covid vaccines.”

The Biden administration has defended its global response, with officials announcing last week that the United States has sent more than 110 million doses of vaccine to dozens of nations. The United States also is moving to distribute 500 million doses of mRNA vaccine that the administration purchased from Pfizer and plans to share with nearly 100 low- and middle-income nations.

“From the beginning of my presidency, I’ve been very clear-eyed that we need to attack this virus globally, not just at home, because it’s in America’s self-interest to do so,” Biden said last week, pledging that the United States would serve as “the arsenal of vaccines, just as we were the arsenal of democracy during World War II.”

Activists and watchdogs say the administration needs to go much further. Some of their frustration has centered on Moderna, which received more than $1.3 billion in federal funding to produce its vaccine but, they argue, has done too little to share its expertise with others.

“This administration has been playing footsies with Moderna instead of leading on this issue,” Staley added, invoking Biden’s comparison of the fight against the pandemic to World War II. “Do you think Roosevelt asked Henry Ford if he could start building tanks, but only on the company’s timetable?”

The watchdog group Public Citizen also argued Tuesday that Biden has sweeping powers to share details of Moderna’s vaccine production process, citing the April 2020 contract that Moderna signed with the Biomedical Advanced Research and Development Authority, an arm of the Department of Health and Human Services.

“The knowledge that can help end the pandemic should not be a secret,” said Zain Rizvi, a law and policy researcher who authored Public Citizen’s report and concluded that the federal government retains “unlimited rights” to data first produced under that contract. “The Biden administration promised a wartime response to the global vaccine effort. It’s time to deliver.”

A spokesperson for Moderna did not immediately respond to a request for comment.

In their letter to Biden, the experts demanded that the administration commit to establishing 8 billion doses per year of mRNA vaccine capacity by the end of the year, exporting at least 40 million vaccine doses from the United States per month and helping set up vaccine manufacturing hubs around the globe.

Global health experts last month said in a review that global vaccine production is projected to exceed 7 billion doses this year and that wealthy countries have pledged to share nearly 1 billion with the developing world. But many of the doses set to be produced — and shared so far — are not messenger RNA (mRNA) vaccines, which have been found to produce greater levels of protection.

“People are really frantic right now,” said Yale University public health researcher Gregg Gonsalves, who co-signed the letter and said that he had privately urged administration officials to take immediate action. “I think you’re going to see an escalation from our side over the next few weeks. No one seems to have gotten the message that the world is burning — and the status quo is unacceptable.”