Domestic drugmaker Sinopharm's two vaccines are both more than 70 percent effective against symptomatic cases of COVID-19, according to a study published on Wednesday on the world's first third-stage clinical trial of inactivated vaccines.

The vaccine, developed by a Beijing unit of Sinopharm's China National Biotech Group, has 78.1 percent efficacy against symptomatic cases of COVID-19, while the vaccine made by the group's unit in Wuhan, Hubei province, has 72.8 percent efficacy, according to the study results released online by The Journal of the American Medical Association.

The study also marks the first time a domestic COVID-19 vaccine maker had released third-stage trial data in a peer-reviewed international journal, the company said in a statement on Thursday.

Both the vaccines require two doses to complete inoculation. They use a weakened form of the coronavirus to trigger an immune response.

The trial was initiated in mid-July and involved more than 40,400 people in the United Arab Emirates and Bahrain. It was conducted in a randomized, double-blind method that is considered the gold standard for human trials.

About one-third of participants in the trial were given the vaccine from the Beijing unit, one-third from the Wuhan unit and the remainder were given a placebo.

Interim analysis of the trial shows that treatment of adults with either of the inactivated SARS-CoV-2 vaccines "significantly reduced the risk of symptomatic COVID-19", the study said.

Both vaccines also demonstrate a good safety record, as the rates of adverse reaction within seven days after an injection were roughly the same among the three groups.

The most common adverse symptoms were pain at the injection site and headache, but they were mild and transient, without need for special treatment. "Serious adverse events were rare," the report said, adding that more data collection for final analysis was ongoing.

Yang Weizhong, executive dean of the School of Population Medicine and Public Health at the Chinese Academy of Medical Sciences & Peking Union Medical College, said the study shows that domestic vaccines had undergone rigorous, science-based trials that meet global standards.

"Real-world use of the vaccines had already attested to domestically developed vaccines' safety and efficacy on many occasions. The study, which is published in a world-renowned journal and has passed peer evaluation, will play a constructive role in deepening the world's understating of China's vaccine products, and it is expected that more countries and regions across the globe will use our doses," Yang said.

The vaccine from the China National Biotech Group's unit in Beijing was the first to gain conditional market approval from the top drug regulator on Dec 31. On May 7, it was granted emergency use by the World Health Organization, making it the first domestic COVID-19 vaccine to obtain the green light to streamline its distribution overseas, particularly in middle and lower-income countries.

The vaccine from the institute in Wuhan was approved for public use in China on Feb 25.

China had administered 566.7 million doses of COVID-19 vaccines as of Wednesday, data from the National Health Commission shows. In addition to the two vaccines from Sinopharm, three other domestic vaccines have been rolled out.

The new study also noted that more research and data are needed to evaluate Sinopharm vaccines' efficacy in protecting pregnant women, people younger than 18, as well as high-risk groups including those with chronic diseases and the elderly.

Their efficacy in preventing severe cases and asymptomatic infections and the length of immunity also require further tests, it added.

Yang Xiaoming, chairman of the China National Biotech Group and an expert on China's vaccine research and development task force, said at a forum on Thursday that preliminary studies show that its vaccines can also protect against COVID-19 variants that first emerged in the United Kingdom and South Africa.

He said the company is scaling up its production rapidly and is aiming to reach a capacity of 3 billion doses annually by the end of next month. Sinopharm has supplied vaccines to about 80 countries and regions across the globe, and more than 100 countries have raised procurement requests.

As the mass vaccination campaign is progressing smoothly nationwide, Yang said China is projected to vaccinate 560 million people by the end of next month and 70 to 80 percent of its population by October.