A staff member displays samples of the COVID-19 inactivated vaccine at Sinovac Biotech Ltd., in Beijing, capital of China, March 16, 2020. (ZHANG YUWEI / XINHUA)

BEIJING - Four Chinese COVID-19 vaccine candidates have started international phase-3 clinical trials, according to the State Council joint prevention and control mechanism against COVID-19.

Phase-3 clinical trials usually involve thousands of people to verify the safety and effectiveness of the vaccines, which are key to their market approval

Some of the phase-3 trials are expected to complete the first round of vaccinations in early September, with preliminary data expected as early as November.

Phase-3 clinical trials usually involve thousands of people to verify the safety and effectiveness of the vaccines, which are key to their market approval.

As the epidemic has been under control in China, the country no longer has conditions for large-scale clinical trials, so all the phase-3 trials are being carried out overseas.

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Two inactivated COVID-19 vaccines developed by the China National Biotec Group (CNBG) have been approved for phase-3 clinical trials in several countries in the Middle East and South America, involving more than 30,000 people, according to Yang Xiaoming, president of the CNBG.

An inactivated COVID-19 vaccine developed by Sinovac Biotech Co., Ltd. is undergoing phase-3 clinical trials in some countries in South America and Southeast Asia, according to Yin Weidong, chairman and CEO of Sinovac.

A recombinant COVID-19 vaccine with the modified defective adenovirus as the vector is also undergoing phase-3 trials.

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According to a guideline for the clinical evaluation of COVID-19 vaccines recently released by the National Medical Products Administration, the vaccine should provide immunity for at least six months, preferably for more than a year.