Brazilian health officials say a Chinese coronavirus vaccine has demonstrated an overall efficacy rate of 50 per cent, far lower than originally indicated in a blow to one of the Latin American nation’s hopes for defeating the pandemic. 

The S?o Paulo-based Butantan Institute said last week that the CoronaVac vaccine, developed by China’s Sinovac Biotech, was 78 per cent effective at preventing mild infections, and 100 per cent effective for moderate and serious cases that require hospitalisation or intensive care.

However, following criticism over a lack of transparency and details in the results, the institute announced fuller data on Tuesday that showed that CoronaVac’s general efficacy rate fell to 50.4 per cent when “very mild” cases were included.