A Chinese research team conducted a phase 2 clinical trial of a COVID-19 candidate vaccine which found the vaccine to be safe and able to induce an immune response, according to the team's paper published in the British medical journal The Lancet on 20 July.

The team, headed by Academician Chen Wei from the Academy of Military Medical Sciences of the Academy of Military Sciences and Professor Zhu Fengcai from Jiangsu Provincial Center for Disease Control and Prevention, had previously finished the phase 1 trial of the vaccine and published the relevant results.

The related trials assessed a recombinant adenovirus type-5 (Ad5) -vectored COVID-19 vaccine. According to the paper, the phase 2 clinical trial conducted in China involved more than 500 volunteers including people aged over 55, a scale of broader participation than the phase 1 trial. The experiment sought to evaluate the vaccine's ability to induce immune responses in the human body and its safety level. The results turned out to be positive in both terms.

Zhu says in a news release by The Lancet that the phase 2 trial adds further evidence on safety and immunogenicity in a larger population than the phase 1 trial, an important step in evaluating a candidate vaccine. Phase 3 trials are now underway.

The researchers also noted that as no participants were exposed to SARS-CoV-2 virus after vaccination, it is not possible for this study to determine whether the candidate vaccine effectively protects against SARS-CoV-2 infection, which will have to be evaluated in a phase 3 clinical trial.

According to The Lancet, there are about 250 candidate vaccines against SARS-CoV-2 in development worldwide, among which at least 17 are currently under evaluation in clinical trials.