SHANGHAI: China's CanSino Biologics said on Wednesday (Sep 9) that expert opinion on its high-profile COVID-19 vaccine candidate should not be followed “blindly” without sufficient clinical trial data.
Scientists outside the company have expressed concern that the effectiveness of CanSino's candidate Ad5-nCoV, which is based on a common cold virus to which many people have been exposed, could be limited. They said existing antibodies against the common cold virus might undermine Ad5-nCoV.
“Vaccine development is a practice-based science, and we should not blindly follow experts,” Zhu Tao, chief scientific officer, said during an investor conference.
He said there were instances in which vaccines created using methods doubted by experts had obtained regulatory approvals after clinical trials proved they worked.
No evidence showed that existing antibodies against the common cold could have a major adverse impact on Ad5-nCoV’s ability to trigger antibodies against the coronavirus, Zhu said, citing results from 128 participants tested with a lower dose of the vaccine candidate in a mid-stage trial.
Ad5-nCoV, still in final-stage trials, has been approved for use in the Chinese military.
Vaccine companies normally have to collect data in large-scale, late-stage trials to obtain regulatory approval for mass use.
It is unscientific to compare the antibody levels generated by different vaccine candidates so far, because varied testing methods could distort results, Zhu said.
AstraZeneca on Tuesday said it paused a late-stage trial of its leading experimental viral vector-based vaccine, which uses a technology similar to CanSino's, after an unexplained illness in a study participant.
The hiccup does not mean all viral-vector based experimental vaccines are risky, Zhu said, adding that it was not rare for clinical trials to be paused.