Chinese-made ZF2001 COVID-19 vaccine was found to be well tolerated, without causing any vaccine-related serious adverse events in its phase 1 and 2 trials, according to an article published on The Lancet website Wednesday. 

The vaccine was jointly developed by the Institute of Microbiology of Chinese Academy of Sciences (IMCAS) and Anhui Zhifei Longcom Biopharmaceutical. 

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In the phase 1 trial, involving about 50 participants, no vaccine-related serious adverse events were reported, according to the article. 

In the phase 2 trial, involving some 900 participants, seven reported serious adverse events - one in the two-dose 25 μg vaccine group, one in the two-dose 50 μg vaccine group, two in the three-dose placebo group, one in the three-dose 25 μg vaccine group, and two in the three-dose 50 μg vaccine group. But none was considered vaccine related, said the article. 

On the two-dose schedule, seroconversion rates of neutralizing antibodies 14 days after the second dose were 76 percent (114 of 150 participants) in the 25 μg group and 72 percent (108 of 150) in the 50 μg group, the article showed. 

On the three-dose schedule, seroconversion rate of neutralizing antibodies 14 days after the third dose were 97 percent (143 of 148 participants) in the 25 μg group and 93 percent (138 of 148) in the 50 μg group.

China approved the ZF2001 vaccine for emergency use on March 10. The late-stage clinical trial has started in several countries, including Uzbekistan, Pakistan, Ecuador, Indonesia, as Uzbekistan already approved its use on March 1.