CanSino Biologics Inc's vaccine was 57.5 per cent effective against symptomatic Covid-19 and 91.7pc against severe disease four weeks or longer after one dose, while its protection appeared lower in older people, peer-reviewed results from a large trial showed, according to Reuters.

The single-shot Ad5-nCoV vaccine, which CanSinobio co-developed with the Chinese military-backed Beijing Institute of Biotechnology, has been approved for use in countries such as Mexico and Pakistan.

The efficacy of 57.5pc against symptomatic Covid-19, meaning it reduced the risk of symptomatic disease by 57.5pc for vaccinated people as compared with the unvaccinated, came from analysis of 150 cases in a cohort of over 20,000 healthy adults in a Phase III clinical trial, wrote researchers.