The United Arab Emirates issued the first government approval of a Chinese coronavirus vaccine on Wednesday, citing preliminary data showing that it was 86 percent effective, a move that could bring Chinese vaccines a step closer to widespread use.

The announcement by the Emirates’ Ministry of Health and Prevention was the first official indicator of a Chinese vaccine’s potential to help stop the pandemic. If results from elsewhere show similar findings, the Chinese vaccines could offer a lifeline to developing countries that cannot afford vaccines from the United States that are likely to be more expensive and more difficult to transport.

But Chinese officials and Sinopharm, the state-owned maker of the vaccine, were silent on Wednesday on the Emirati disclosures. And scientists noted that the announcement was lacking in data and other critical details.

The news that a Chinese vaccine is 86 percent effective — exceeding the 50 percent threshold set by many governments — is a boost to China’s biomedical ambitions. But it falls short of the performance reported by the American drug makers Pfizer and Moderna, which said earlier that their vaccines were more than 90 percent effective at protecting against the coronavirus.

The Emirates, which is among 10 countries where Sinopharm is testing its two vaccines, said it had reviewed an interim analysis of data from late-stage clinical trials by Sinopharm that also showed the vaccine was 100 percent effective in preventing moderate and severe cases of the disease. There were no serious safety concerns, it said.

“The announcement is a significant vote of confidence by the U.A.E.’s health authorities in the safety and efficacy of this vaccine,” the ministry said in a release carried by the state-run Emirates News Agency. The government did not say whether it had conducted an independent analysis of the raw data.

The data from the Emirates bodes well for Sinopharm’s vaccines to obtain full regulatory approval in China, which Sinopharm sought even before the completion of final trials. The company is also conducting trials in Bahrain, Jordan, Peru, Argentina and elsewhere.

“I think it could hit the market in China very soon, and there will be news within the next one to two weeks,” said Tao Lina, a vaccine expert in China and a former immunologist at the Shanghai Center for Disease Control and Prevention.

The vaccine could also help bring China closer to fulfilling a pledge by China’s top leader, Xi Jinping, to make the vaccine a “global public good.”

But even as the announcement by the Emirates raised hopes about the promise of Chinese vaccines, it also pointed to a frustrating lack of clarity that has dogged China’s coronavirus vaccine development for months.

Sinopharm would not confirm or comment on the Emirates news even hours after it came out. A spokeswoman for the company hung up the phone when reached and did not respond to messages and calls afterward.

The news release from the Emirati government provided few other key details, such as the number of Covid-19 cases that were analyzed or the ages of the volunteers, making it unclear to scientists how Sinopharm came to its conclusions.

“The devil is in the details,” said Beate Kampmann, director of the Vaccine Center at the London School of Hygiene and Tropical Medicine. “It’s very difficult to judge this without seeing the number of cases. The main thing is, the trial results need to be made public.”

Jin Dongyan, a virologist at the University of Hong Kong, called the information in the Emirates’ disclosure “mediocre,” saying more transparency from the vaccine maker was needed.

“If they make everything secretly, like a black box, that does not help,” Professor Jin said. “That would just create confusion and mistrust and could be counterproductive.”

The need for clarity on the safety and efficacy of China’s vaccines has taken on more urgency after Sinopharm revealed it had already vaccinated roughly a million people even before the completion of clinical trials. The campaign has alarmed overseas scientists who say it exposes people to undue risks.

Chinese officials have repeatedly assured the public that the country’s coronavirus vaccines are safe, while providing few details. Last month, Liu Jingzhen, the chairman of Sinopharm, said no one among the people who had received the company’s vaccines had experienced any adverse reactions. He said that “only a few had mild symptoms.”

In October, Zheng Zhongwei, a senior health official, said the government had established a “follow-up program” to track the people who had been vaccinated, though he gave no details.

Sinovac Biotech, a Beijing-based private vaccine maker, has already begun exporting its vaccines to countries like Indonesia and Brazil. Sinopharm, which has another vaccine in late-stage testing, has said it is preparing to deliver 500 million doses worldwide, according to the state-run newspaper Science and Technology Daily.

It is unclear whether the Emirates will start using the Chinese vaccine — which Sinopharm developed with the Beijing Institute of Biological Products — for mass inoculations. The government had already approved the vaccine for emergency use in September for frontline workers at risk of contracting Covid-19.

Some other countries where Sinopharm is conducting trials are counting on Chinese vaccines to help protect their populations. Morocco says it is preparing to vaccinate 80 percent of its adults, relying initially on a Sinopharm vaccine, though it would wait for China to approve the vaccine, according to Médias24, a Moroccan news website.

The Chinese vaccines are also appealing to developing countries because they could be easier to distribute. Sinopharm has said its vaccines need be refrigerated at temperatures of only 2 to 8 degrees Celsius (or 35 to 46 degrees Fahrenheit) and could remain stable for up to three years. In contrast, Pfizer and Moderna’s vaccines, which are made with genetic materials that fall apart when they thaw, require industrial freezers, making transportation and storage more challenging.

Sinopharm’s vaccines are both made from coronaviruses that have been killed or weakened, a technique that has been used for decades in the influenza and polio vaccines, for example. By comparison, Moderna’s and Pfizer’s vaccines use a technology that has never before been approved for widespread use.

Another advantage of the inactivated vaccines being developed by Sinopharm is that they tend to have fewer adverse effects after immunization, according to Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York. He said more clarity on the trials in the Emirates would be welcome, but expressed confidence in the vaccine’s initial results.

“It would be great to see some of that data,” Professor Krammer said in an email. “But 86 percent is a respectable number — there is absolutely nothing wrong with that. I would take such a vaccine.”

Aida Alami and Elsie Chen contributed reporting.