By Drew Hinshaw in Geneva and Chao Deng in Taipei

GENEVA -- The World Health Organization called Tuesday for $50 billion in funding from wealthy nations to buy vaccine doses for developing countries, saying that "countless lives" and trillions of dollars in economic activity hang in the balance.

The WHO also endorsed a second Chinese vaccine against Covid-19, CoronaVac, a shot by private pharmaceutical firm Sinovac BioTech Ltd. for emergency use. The decision paves the way for a WHO-backed Covax vaccine pool to distribute doses. The moves are part of a renewed push by the United Nations to get more vaccines to the developing world to bring global contagion under control.

They came a day after the agency ended an annual meeting with some of its other efforts -- such as research into the origins of the disease or a new treaty to stop future pandemics -- snagged by disagreements between the U.S. and China.

Joined by leaders of the World Bank, the World Trade Organization and the International Monetary Fund, WHO's Director-General Tedros Adhanom Ghebreyesus asked that wealthy countries donate $50 billion that he said would be enough to have 60% of the world-wide population covered within the next year. That, leaders of the four institutions said, would allow $9 trillion in new economic growth by 2025.

"It is now crucial to get these lifesaving tools to the people who need them quickly," Dr. Tedros told reporters. "We have the means to end this pandemic quickly and save countless lives and livelihoods, but we need the will to make it happen."

The WHO's vaccine push comes as the U.S. and China are sharply divided over some of the other major issues facing the agency. An effort to understand how the virus first emerged is bogged down in talks, with the U.S. pushing for independent experts to be a part of the research mission. China says the mission should now focus on other countries.

A new global pandemic treaty that could give the WHO more power to swiftly investigate new and threatening outbreaks faces opposition from China, which is disinclined to give the agency such authority. It also drew concerns from the U.S., which would need congressional approval to sign onto a treaty.

Meanwhile, the WHO has focused on supplying vaccines to the developing world, where it does much of its ordinary work. The agency is particularly asking Group of Seven countries to raise their funding for vaccine donations when they meet in the U.K. this month.

With adequate funding, manufacturers could produce enough doses to immunize 60% of the world's population by the first half of next year, the WHO said Tuesday. Without it, poorer countries will continue to see outbreaks that could allow new variants to arise, the agency said.

They will also lose out on recovering as quickly as more vaccinated countries in North America, Europe and Asia, said IMF Managing Director Kristalina Georgieva.

"A two track pandemic is causing a two track economic recovery," she said. "Our data shows that in the near term, vaccinating the world is the most effective way to boost global output."

By now, the WHO-backed Covax effort, a vaccine sharing pool to help the world's poorest countries, was meant to have vaccinated the entire healthcare population of the developing world. But an outbreak in India has prompted the government there to curb exports, a blow to the effort, which was counting on the Serum Institute of India to supply it with badly needed doses.

The WHO's authorization for emergency use of the CoronaVac vaccine is expected to help relieve vaccine shortages, once Covax and Sinovac can reach an agreement to distribute doses into countries that need them.

Last month, WHO listed China's flagship Covid-19 vaccine, made by state-owned Sinopharm, for emergency use.

Both Chinese vaccines have lower efficacy rates than shots made by Pfizer Inc. and Moderna Inc., according to preliminary clinical data. The WHO cited CoronaVac efficacy results showing the vaccine prevented symptomatic disease in 51% of those vaccinated and prevented severe Covid-19 and hospitalization in 100% of participants in trials.

But it isn't clear how many doses either Chinese vaccine manufacturer can deliver to Covax or when. "We urge manufacturers to participate in the Covax Facility, share their know-how and data and contribute to bringing the pandemic under control," said Dr. Mariângela Simão, WHO assistant-director general for access to health products.

Dongyan Jin, a molecular virologist and professor at the University of Hong Kong, said before WHO's announcement that an approval would speak more to the need for additional vaccines rather than represent a vote of confidence. He said questions about the reliability of some of Sinovac's earlier clinical data remain, given a lack of details from the firm and researchers for the trials.

While Turkey and Indonesia have reported higher efficacy rates for preventing Covid-19 symptoms of 83.5% and 65%, respectively, in their clinical trials, health experts have given less weight to the figures given limited sample sizes. The Indonesian trial, for example, had just roughly 1,620 participants.

In Brazil, which ran the most comprehensive trial -- involving nearly 13,000 participants, including people older than 60 -- CoronaVac's efficacy in a clinical trial of healthcare workers was found to be 50.38% against symptomatic infections -- just enough to meet the WHO's 50% standard.

Kim Mulholland, a pediatrician in Melbourne and member of an independent committee that advised WHO on CoronaVac, said the low efficacy rate in Brazil was likely because the healthcare workers in the trial had more access to testing than elsewhere, a point that Sinovac made to the committee during its assessment. The Brazil study also contained a number of cases that were classified as very mild, skewing the rate lower, he said.

Sinovac hasn't directly released its study results, in contrast to Western vaccine makers who tightly control their trials and have published details in peer-reviewed medical journals.

Instead, Sinovac's results have largely been made public by governments that in some cases were under pressure to approve vaccines for emergency use fast to fight the pandemic.

"It rolled out in a very messy way," said Jerome Kim, director of the International Vaccine Institute, a nonprofit based in Seoul. He explained that Sinovac often didn't offer public explanations when governments revised the data they had released, contributing to questions about whether the data was intended to be definitive.

The most promising sign of CoronaVac's effectiveness comes from Serrana, a Brazilian town with 45,000 people. Deaths from the disease fell 95% between the beginning of February and mid-May, according to a presentation Monday by Butantan Institute, the São Paulo-based public-research center that organized the study with Sinovac. The number of symptomatic cases fell 80%, and hospitalizations related to the disease dropped 86%.

In other retrospective studies, Indonesia and Chile have shown CoronaVac to have moderate to high levels of effectiveness after two doses. Data through April released by Chilean authorities indicates CoronaVac is roughly 65% effective in preventing symptomatic infection, 85% effective against hospitalization and 89% effective in preventing severe cases.

Indonesian regulators said last month that CoronaVac was 94% effective in preventing Covid-19 symptoms and 98% effective at preventing deaths, based on data involving roughly 120,000 health workers.

Despite the high effectiveness figures, some Indonesian epidemiologists have pointed to flaws in the study's design, which didn't account, for instance, for whether subjects receiving vaccinations may have been healthier to start with.

"It's very difficult to make inferences or to make conclusions from this kind of data," said Pandu Riono, an epidemiologist at the University of Indonesia.

A spokeswoman for Indonesia's health ministry acknowledged the data wasn't as good as that from a controlled clinical trial but said the goal was to present available data on the effectiveness of the vaccine among health workers. The data was supplied by hospitals and medical clinics in the capital, Jakarta, she added, and Sinovac wasn't involved in its release.

--Jon Emont contributed to this article.

Write to Drew Hinshaw at drew.hinshaw@wsj.com and Chao Deng at Chao.Deng@wsj.com

(END) Dow Jones Newswires

06-01-21 1641ET