CoronaVac, an inactivated COVID-19 vaccine developed by China's Sinovac Biotech Ltd., was shown to be 50.7% effective against symptomatic COVID-19 cases, according to new trial results revealed by Brazil's state-run Butantan Institute on Sunday.

The jab was also found to be equally effective against the two coronavirus variants known as P.1 and P.2, which were populated in Brazilian cities including Manaus and Rio de Janeiro.

The study, which the institute said had been sent to the medical journal The Lancet for publication, tested 12,400 volunteers across Brazil.

Malaysia said on Monday that it will begin vaccinating its elderly population with China's Sinovac jab starting next Monday, when phase two of its national immunization program starts.