The world comes together for a virtual vaccine summit. The U.S. is conspicuously absent.

LONDON — World leaders came together in a virtual online summit Monday to pledge billions of dollars to quickly develop vaccines and drugs to fight the coronavirus.

Missing from the roster was the Trump administration, which declined to participate, but highlighted from Washington its “whole-of-America” efforts underway in the United States and its generosity to global health efforts.

The conference, led by European Commission President Ursula von der Leyen and a half-dozen countries, was set to raise $8.2 billion from governments, philanthropies and the private sector to mass-produce drugs, vaccines and testing kits to combat the virus that has killed nearly 250,000 people worldwide.

With the money came soaring rhetoric about international solidarity, and a good bit of boasting about each country's efforts and achievements, live and prerecorded, by Germany's Angela Merkel, France's Emmanuel Macron, Britain's Boris Johnson, Japan's Shinzo Abe — alongside Israel's Benjamin Netanyahu and Turkey's Recep Erdogan.

"The more we pull together and share our expertise, the faster our scientists will succeed," said Johnson, who was so stricken by the virus that he thought he might never leave the intensive care unit alive last month. "The race to discover the vaccine to defeat this virus is not a competition between countries but the most urgent shared endeavor of our lifetimes."

A senior Trump administration official said Monday the United States "welcomes" the efforts of the conference participants. He did not explain why the United States did not join them.

"Many of the organizations and programs this pledging conference seeks to support already receive very significant funding and support from the U.S. government and private sector," said the official, who spoke on the condition of anonymity under State Department rules for briefing reporters.

Public health officials and researchers expressed surprise.

"It's the first time that I can think of where you have had a major international pledging conference for a global crisis of this kind of importance and the U.S. is just absent," said Jeremy Konyndyk, who worked on the Ebola response in the Obama administration.

Given that no one knows which vaccines will succeed, he said, it's crucial to back multiple efforts working in parallel.

"Against that kind of uncertainty we should be trying to position ourselves to be supporting — and potentially benefiting from — all of them," said Konyndyk, a senior policy fellow at the Center for Global Development. "And instead we seem to be just focused on trying to win the race, in the hopes we happen to get one of the successful ones."

Conference participants expressed a need for unity.

“We can’t just have the wealthiest countries have a vaccine and not share it with the world,” Canadian Prime Minister Justin Trudeau said.

"Let us in the international community unite to overcome this crisis," Japan's Abe said.

Russia and India also did not participate. Chinese premier Li Keqiang was replaced at the last minute by Zhang Ming, Beijing's Ambassador to the European Union.

The U.S. official said the United States "is the single largest health and humanitarian donor in world. And the American people have continued that legacy of generosity in the global fight against COVID-19."

"And we would welcome additional high-quality, transparent contributions from others," he said.

Asked three more times to explain why the United States did not attend, the official said he already had given an answer.

The U.S. government has provided $775 million in emergency health, humanitarian, economic and development aid for governments, international organizations and charities fighting the pandemic. The official said the United States is in the process of giving about twice that amount in additional funding.

There was one major American player at the virtual summit: The Bill & Melinda Gates Foundation, which promised to spend $125 million in the fight.

"This virus doesn't care what nationality you are," Melinda Gates told the gathering. As long as the virus is somewhere, she said, it's everywhere.

Scientists are working around the clock to find a cure or treatment for COVID-19. The World Health Organization says eight vaccines have entered human trials and another 94 are in development.

But finding an effective vaccine is only part of the challenge. When it's discovered, infectious disease experts are predicting a scramble for limited doses, because there won't be enough to vaccinate everyone on Day One. And deploying it could be difficult, particularly in countries that lack robust medical infrastructure.

Those that have begun human trials include a research project at Oxford University in England, which hopes to have its vaccine ready in the fall. The university started human trials on April 23. "In normal times," British Health Secretary Matt Hancock said, "reaching this stage would take years."

» FAQ: Your coronavirus questions, answered.

Other scientists are sprinting to create antiviral drugs or repurposing existing drugs such as remdesivir, which U.S. infectious diseases chief Anthony S. Fauci said he expected would be the new "standard of care."

Other approaches now in trial include treatments such as convalescent plasma, which involves taking blood plasma from people who have recovered from COVID-19 to patients who are fighting the virus, in the hope that the antibody-rich fluid will give the infected a helping hand.

Conference participants expressed hope that by working together, the world will find solutions more quickly — and they can then be dispersed to all countries, not only the wealthy, or those that developed vaccines first.

Many of the leaders stressed their support for the World Health Organization. President Trump announced last month he was cutting off U.S. funding for the WHO because he said the organization had sided too closely with China, where the coronavirus arose. Trump says Chinese leaders underplayed the threat and hide crucial facts.

Public health analysts have shared some of those criticisms, but have also criticized Trump for cutting off funding.

Peter Jay Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, said the United States has always been the primary funder of new products for global health. The country invested $1.8 billion in neglected diseases in 2018, according to Policy Cures Research, more than two-thirds of the worldwide total.

Hotez said the United States shoulders the burden of investing in global health technologies, while countries such as China do not step up.

"More than one mechanism for supporting global health technologies — that may not be such as a bad thing," he said. "If it was all under one umbrella, you risk that some strong-willed opinions would carry the day and you might not fund the best technology."

Hotez is working on a COVID-19 vaccine that uses an existing, low-cost technology, previously used for the hepatitis B vaccine, precisely because he is worried about equitable distribution of vaccine.

"I'm not very confident that some of the cutting-edge technologies going into clinical trials, which have never led to a licensed vaccine before, are going to filter down to low- and middle-income countries anytime soon," Hotez said. "I'm really worried."

____

Johnson and Morello contributed from Washington. The Washington Post’s Karla Adam in London and Adam Taylor in Washington contributed to this report.