TAIPEI, Taiwan — China said Friday that it will join a World Health Organization-backed effort to distribute vaccines for the novel coronavirus, boosting a ­major public health initiative the White House pointedly rejected.

More than 150 countries have agreed to participate in the Covid-19 Vaccines Global Access Facility, or Covax, which aims to develop and distribute 2 billion doses of a vaccine by the end of 2021.

Under the plan, rich and poor countries pool money to provide manufacturers with volume guarantees for a slate of potential vaccines. The aim is to discourage hoarding and focus on vaccinating high-risk people in every participating country first.

Some big, wealthy players — including the European Union, Japan and Britain — signed on. But the White House said it would not participate, in part because it won't work with the WHO. China and Russia also declined to join by the deadline.

China's reversal will bolster the multilateral effort. It also gives Beijing a chance to cast itself as a leader in public health at a time when its reputation is suffering — and the United States is stepping back.

"This is a win for them in terms of credibility and influence," said J. Stephen Morrison, director of the Global Health Policy Center at the Center for Strategic and International Studies. "A big win."

Since the outset, the vaccine race has been dominated by rich countries cutting deals directly with drugmakers, rather than working collaboratively.

The three co-leaders of the initiative — the WHO, the vaccine alliance Gavi, and the Coalition for Epidemic Preparedness Innovations — have spent the last few months urging wealthy countries to cooperate.

In May, Chinese President Xi Jinping pledged $2 billion to tackle the pandemic and promised that China's coronavirus vaccine would be "a global public good."

But in the months that followed, Beijing appeared focused on securing doses for domestic use, as well as wooing strategic allies such as the Philippines and Pakistan with the promise of early doses.

Now, its strategy is shifting. Though the exact terms have not been released, it seems Beijing will be able to continue pursuing bilateral deals while also participating in Covax, potentially getting Chinese vaccines to more countries.

In a statement announcing the deal, Chinese Foreign Ministry spokeswoman Hua Chunying said China is confident it could ramp up manufacturing. "We are taking this concrete step to ensure equitable distribution of ­vaccines, especially to developing countries, and hope more-capable countries will also join and support Covax," Hua said.

Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations, said the decision appeared to be driven, at least in part, by recent criticism of China's pandemic response and questions about the safety of its vaccine trials.

"China's international reputation has really been tarnished by covid," Huang said. "They are responding to international criticism."

Whatever the reason, the turnaround could have a very real impact — on China's image and on efforts to combat the coronavirus.

"You can have good public relations, an attempt at soft-power diplomacy, and it can still be good — it doesn't inherently undermine the commitment," said Alexandra Phelan, a global health lawyer at Georgetown University's Center for Global Health Science and Security.

“If China doesn’t follow up and commit funding, then sure, it is a PR move,” she continued. Either way, China is sending “a strong message about a commitment to an international multilateral effort and commitment to vaccines as global public goods.”

China's move is particularly striking because of what is happening in the United States.

The White House said last month that it would not join Covax because it did not want to be "constrained by multilateral organizations influenced by the corrupt World Health Organization and China."

The Trump administration has signaled its intent to withdraw from the U.N. agency, accusing WHO officials of repeating Chinese government talking points and praising Beijing’s response to the pandemic despite Chinese officials’ missteps and coverups in the crucial early days.

Rather than join forces with other countries or organizations, the United States has focused on developing a vaccine as quickly as possible with an eye on vaccinating every American, including those at low risk, before assisting anyone else.

“We have seen the U.S. withdraw from any kind of global role in this pandemic, ensuring vaccine and drug supply for itself but without regard for other countries,” said Suerie Moon, co-director of the Global Health Center at the Graduate Institute of International and Development Studies in Geneva.

Officials from China’s Center for Disease Control said a Chinese vaccine could be ready for general public use as early as November. The country’s National Health Commission said China can produce up to 610 million vaccine doses in 2021 and more than 1 billion in 2022.

But China’s efforts to roll out a vaccine quickly — and the government’s unusual disclosures that hundreds of thousands of people have already received vaccines before they have passed clinical trials — has drawn criticism from researchers and ethicists concerned about safety.

China has four vaccines in Phase 3 clinical trials, including one co-developed at a military research institute that has already been administered to soldiers and overseas state employees.

Russia’s Gamaleya Research Institute and Britain’s AstraZeneca both have vaccines in the last stage of trials, as do American firms Moderna, Johnson & Johnson and Novavax.

Jerome Kim, head of the International Vaccine Institute, an independent nonprofit founded as part of the U.N. Development Program, said that it was important that China was showing “solidarity and support” for the fight against the coronavirus, but that the announcement is just a start.

“Importantly now, the three organizations that lead Covax have to work to ensure that the Chinese commitment can be fully realized — that the vaccine from Chinese manufacturers will meet WHO prequalification standards; that it is safe and effective and, importantly, can be provided at a reasonable cost,” Kim said.