An inhaled version of CanSino Biologics' (CanSinoBio) Covid-19 vaccine triggered immune responses without serious side effects, an early-stage clinical trial showed.

The two-dose candidate requires lower dosages than the injected version and could help CanSinoBio boost its production capacity, the company's chief executive said in April.

Two inhaled doses of the Ad5-nCoV vaccine, given 28 days apart, elicited similar level of neutralising antibodies to those of a single injection, according to a peer-reviewed paper.

The readings are based on data from a Phase I trial involving 130 healthy adult participants in China and published in the medical journal, The Lancet Infectious Diseases.