China's top epidemiologist Zhong Nanshan. [File photo provided to chinadaily.com.cn]

Chinese vaccines are 100 percent effective in preventing serious COVID-19 symptoms from Delta variant of the coronavirus, a prominent Chinese respiratory disease expert said.

Research results have also proved that domestically developed vaccines are 76.9 percent effective in preventing moderate symptoms, 67.2 percent effective against acquisition of mild symptoms and 63.2 percent effective in preventing a patient from becoming an asymptomatic carrier, said Zhong Nanshan, director of the Guangzhou Laboratory and the National Clinical Research Center for Respiratory Diseases.

Zhong, an academician of the Chinese Academy of Engineering, noted the figures in his keynote speech at the annual conference of Respiratory Diseases of the Guangdong Medical Association in Guangzhou, Guangdong province, in late July.

China now has nine vaccines that have entered their third stage of clinical trials, and seven of those have been approved for use, Zhong said.

Although the outbreak of COVID-19 in Guangdong has basically been brought under control, more concrete measures should be introduced, Zhong said. He urged residents across the country to get vaccinated against the coronavirus, and he called for sustained international collaboration in the battle against the pandemic in the weeks ahead.

"No country is safe until all countries are safe," he said.