Questions have been raised over the effectiveness of a coronavirus vaccine developed by Chinese drug maker Sinovac Biotech after a partner science institute in Brazil, where phase 3 clinical trials are under way, released lower-than-expected efficacy results for the vaccine, The South China Morning Post reported.

The Butantan Institute in Sao Paulo said the CoronaVac vaccine had a roughly 50 per cent general efficacy rate – well below the 78 per cent reported earlier.

The institute said the vaccine was 50.4 per cent effective in preventing Covid-19 with symptoms ranging from mild to severe. The figure, which indicates how effective a vaccine is in trials, just meets the 50 per cent minimum threshold required by most regulators around the world, but is lower than the 70 per cent recommended by the World Health Organization (WHO), the report said.