A total of 508 volunteers, in the second phase trial of the adenovirus vector vaccine, have been administered with injections and are now under observation. If things proceed as planned, the vaccine will be unblinded in May this year, said Chinese military infectious disease expert Chen Wei, during an event on the occasion of China's 34th children's vaccination day, on Saturday.

The adenovirus vector vaccine, which was developed by the research team led by Chen, entered the second phase of clinical tests on April 12 and became the only one in the world to enter the second phase of clinical trials at that time.

Although the COVID-19 epidemic has waned in China, the pandemic globally hasn't reached its turning point, said Chen. "Vaccine could be one of the most powerful weapons to curb the coronavirus currently," Chen was quoted as saying by Beijing Daily on Saturday.

On March 16, the adenovirus vector vaccine that Chen and her team developed was put into clinical trials after approval, and Chen was the first to be administered with the shots. Chen said the vaccine research progressed smoothly, and the data obtained after 7 days and 14 days, both indicated safe.

"The first phase trial is mainly used to prove the safety of the vaccine, while the result in the second phase trial is essential to prove whether the vaccine is efficient," Yang Zhanqiu, deputy director of the pathogen biology department at Wuhan University,  adding that it will indicate how the antibodies react after people receive the vaccine shot.

China is among the top countries across the world, leading the coronavirus vaccine research and development, Yang said. China has adopted five technological approaches to develop COVID-19 vaccines, including inactivated vaccines, recombinant protein vaccines, adenovirus vector vaccines, nucleic acid vaccines, and vaccines using attenuated influenza viruses as vectors.

Also, the inactivated vaccine developed by Chinese institutes entered the second phase of the clinical trial on Friday, becoming the first of its kind globally. The vaccine was developed by Wuhan Institute of Biological Products under the China National Pharmaceutical Group, and the Wuhan Institute of Virology under the Chinese Academy of Sciences.

A total of 96 volunteers in three age groups have received the vaccine in the first phase of the clinical trial as of April 23, according to the developers. So far, it has shown impressive progress, and volunteers are under observation.