What you need to know about the latest updates of COVID-19 vaccines

In recent weeks, a string of vaccine makers including Pfizer, Moderna, and AstraZeneca have released promising phase III trial data, injecting the world with hope that the COVID-19 pandemic will come to an end.

On Wednesday, the U.K. became the first western country to approve a vaccine for COVID-19, authorizing Pfizer to distribute its vaccine on an emergency basis to frontline medical workers and other high-risk groups. The U.S. and the European Union are expected to follow suit in coming days or weeks and give vaccine makers the green light to start distributing their candidates.

But amid the optimism, experts have raised some concerns about the accessibility of Pfizer and Moderna’s candidates, which require costly cold-chain distribution mechanisms, and about the quality of the data provided by British vaccine maker AstraZeneca.

At the same time, China’s two leading vaccine makers—the private Sinovac and state-owned Sinopharm—appear close to rolling out their vaccines in coming weeks with candidates that don’t require expensive cold chain networks.

Western vaccine makers appear to have taken the lead in the global race to produce a vaccine, but Chinese vaccine makers may help fill in the gaps they leave behind.

Sinovac and Sinopharm

Sinovac and Sinopharm have both recently indicated that they are nearing the finish line in the vaccine development process.

Sinovac, which is conducting large-scale clinical trials in Brazil and Indonesia, said last week that it expected to release clinical data from its CoronaVac candidate in Brazil in a matter of days. The Butantan Institute, a vaccine research center and Sinovac’s partner in Brazil, told reporters on Thursday that it expects Sinovac to publish clinical data before Dec. 15. Joao Doria, governor of Brazil’s Sao Paolo state, also said Thursday he aims to begin distributing CoronaVac by January. Sinovac did not respond to Fortune’s request for comment on its trial data.

Sinovac published results of its phase II trial in mid-November that suggest CoronaVac induced immune responses among volunteers and may offer COVID-19 protection. Researchers noted, however, that Pfizer and Moderna’s vaccines induced stronger immune responses.

Meanwhile, on Nov. 25, Chinese state-owned vaccine maker Sinopharm asked regulatory authorities in China to officially make its vaccine available to the Chinese public. In an interview with state-run news outlet Xinhua, a Sinopharm executive did not specify when the company expects to receive a response from Chinese regulators.

Sinopharm has not released any data to the public on its phase III trials, but says it has already distributed the vaccine to nearly a million people in China under the country’s controversial emergency-use program.

Of the two drugmakers’ candidates, Sinovac’s CoronaVac is likely China’s most “promising” vaccine, with the best chances of getting approved and distributed internationally because Sinovac has released more data, says Huang.