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.

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 brought 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.

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.

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.

A total of 10 COVID-19 vaccines have been approved to enter clinical trials in China. In addition to the above four vaccines that have entered phase-3 clinical trials, the rest include recombinant protein vaccines, nucleic acid vaccines and vaccines using attenuated influenza viruses as vectors.

A recombinant protein vaccine jointly developed by the Chinese Academy of Sciences and a biopharmaceutical company in Anhui Province is now undergoing phase-2 clinical trials.

Before mass production, all the vaccines will need to be strictly monitored and evaluated for safety and efficiency.

According to the State Council joint prevention and control mechanism against COVID-19, China approved a trial scheme on June 24 for emergency use of COVID-19 vaccines and gave the green light to two vaccines for emergency use. On July 22, the country officially initiated the emergency use of COVID-19 vaccines.

Zheng Zhongwei, an official of the National Health Commission, said that certain people with high risk of exposure to the virus, and who are unable to take effective protection measures, can receive the emergency vaccination.

However, those who have received the emergency vaccination should also take continuous protective measures.

Medical staff, epidemic prevention workers, immigration officers and those ensuring basic operation of cities are eligible for emergency vaccination.

Some people sent to work overseas have been injected with the inactivated COVID-19 vaccines, along with certain medical personnel and some people working in markets.