A coronavirus vaccine candidate developed by the Chinese Academy of Sciences (CAS) was found to be safe and triggered immune responses in early and mid-stage trials, researchers said on Tuesday. A late-stage trial of the ZF2001 vaccine, which CAS is developing with a unit of Chongqing Zhifei Biological Products , began last month in China. It aims to recruit 29,000 people across China, Uzbekistan, Indonesia, Pakistan and Ecuador. The candidate did not cause serious adverse events, with common mild side-effects including injection pain, redness and swelling, researchers at the Chongqing Zhifei unit, CAS, and other Chinese institutes said in a paper published on Tuesday ahead of peer review. The combined data from Phase 1 and 2 trials involved 950 healthy Chinese participants aged 18-59. Low dose and high dose versions were tested, and the Phase 2 study also tested two doses versus three doses for both the low dose and high dose versions. The higher dose given via three injections spaced 30 days apart did not induce an improved immune reponse compared to the lower dose, the paper said. The Phase 3 trial will look at the lower dose version given over three injections, it said. Neutralising antibodies against the virus were detected among at least 93% participants who received three shots in different groups. The levels of vaccine-triggered antibodies were higher than those seen in samples of patients recovered from the disease, researchers said. However, these antibody-based readings are on their own not sufficient to predict how effective ZF2001 will be in protecting people from the virus, researchers said, warning they could not yet determine the duration of immune responses. The vaccine also triggered moderate cell-based immune responses, a crucial part of the human immune system that works differently from antibodies. ZF2001 is a protein subunit vaccine, which uses a harmless piece of the SARS-CoV-2 virus rather than the entire germ. Four other Chinese vaccines from Sinopharm, Sinovac Biotech and CanSino Biologics have also entered Phase 3 clinical trials.
