The clinical study was to evaluate the safety and immunogenicity for adults aged 18 years and above, the pharmaceutical firm said in a filing to the Hong Kong stock exchange.

The vaccine, called CS-2034, was tested as a booster on people who had received three doses of an inactivated vaccine, it said. Such vaccines, like those made by Sinopharm and SinoVac, are the type used in China.

China has nine domestically-developed COVID vaccines approved for use, but none are based on the messenger RNA technology used in the shots developed by Pfizer-BioNTech and Moderna.

The Chinese shots have also not been updated to target the highly infectious Omicron variant.

CanSino obtained approval to start the clinical trial on mRNA vaccine in April.

(Reporting by Meg Shen; Editing by Josephine Mason and Tomasz Janowski)