They Relied on Chinese Vaccines. Now They’re Battling Outbreaks.

The reason for the surge in Mongolia, Mr. Batbayar said, is that the country reopened too quickly, and many people believed they were protected after only one dose.

“I think you could say Mongolians celebrated too early,” he said. “My advice is the celebrations should start after the full vaccinations, so this is the lesson learned. There was too much confidence.”

Some health officials and scientists are less confident.

Nikolai Petrovsky, a professor at the College of Medicine and Public Health at Flinders University in Australia, said that with all of the evidence, it would be reasonable to assume the Sinopharm vaccine had minimal effect on curbing transmission. A major risk with the Chinese inoculation is that vaccinated people may have few or no symptoms and still spread the virus to others, he said.

“I think that this complexity has been lost on most decision makers around the world.”

In Indonesia, where a new variant is spreading, more than 350 doctors and health care workers recently came down with Covid-19 despite being fully vaccinated with Sinovac, according to the risk mitigation team of the Indonesian Medical Association. Across the country, 61 doctors died between February and June 7. Ten of them had taken the Chinese-made vaccine, the association said.

The numbers were enough to make Kenneth Mak, Singapore’s director of medical services, question the use of Sinovac. “It’s not a problem associated with Pfizer,” Mr. Mak said at a news conference on Friday. “This is actually a problem associated with the Sinovac vaccine.”

Bahrain and the United Arab Emirates were the first two countries to approve the Sinopharm shot, even before late-stage clinical trial data was released. Since then, there have been extensive reports of vaccinated people falling ill in both countries. In a statement, the Bahraini government’s media office said the kingdom’s vaccine rollout had been “efficient and successful to date.”

Still, last month officials from Bahrain and the United Arab Emirates announced that they would offer a third booster shot. The choices: Pfizer or more Sinopharm.

Reporting was contributed by Khaliun Bayartsogt, Andrea Kannapell, Ben Hubbard, Asmaa al-Omar and Muktita Suhartono. Elsie Chen and Claire Fu contributed research.