Clinical trial registry data indicates that researchers plan to start a clinical trial for an additional dose of a COVID-19 vaccine candidate co-developed by China's CanSino Biologics Inc and a military-backed research unit, Reuters news agency reported on Friday.

This new two-dose Phase 1 trial will test the safety of two doses and their ability to generate an immune response, showed a registration record published on 17 September 2020.

A single dose of the vaccine candidate Ad5-nCoV, one among a handful that China is pursuing, has final-stage trials lined up in Pakistan and Russia. The candidate has been approved for use in the Chinese military.

Reportedly, scientists outside the company have expressed concern that the effectiveness of Ad5-nCoV, which uses a common cold virus many people have contracted to carry genetic traces of COVID-19, could be limited.

In response, CanSino had said there was no evidence that existing immunity against the common cold virus could severely hurt Ad5-nCoV's ability to trigger antibodies against COVID-19, citing data gathered from a single dose-based Phase 2 trial.

Subsequently, in July 2020, researchers working on Ad5-nCoV said a flexible additional dose might be able to provide enhanced immune response, based on their previous experience using this method to develop a common cold virus-based Ebola vaccine.

Researchers now expect to recruit 168 healthy adults to take two doses of Ad5-nCoV for the trial estimated to begin on 20 September 2020 in China's Wuhan.