Antibody levels in people inoculated with CanSino Biologics' (CanSinoBIO) single-dose Covid-19 vaccine fell by some 30 per cent after six months, however a booster shot could offer a significant lift, a senior executive said.

The decline in antibodies does not necessarily mean the shots will lose their protection, though how fast they wane could still serve as an important indicator of the immune response, Zhu Tao, chief scientific officer at China's CanSinoBIO, said in an online presentation.

Apart from durable antibodies, researchers have said that other components in a person's immune system, such as T cells and B cell memory, elicited by Covid vaccines may also contribute to protection, according to Reuters.

Six months after being vaccinated with CanSinoBIO's shot, neutralising antibodies were at roughly 70pc of the level seen 28 days after the shot, Zhu said, citing data from 35 vaccinated people.