A coronavirus vaccine developed by China's Sinovac Biotech was 78 percent effective in a late-stage Brazilian trial with no severe Covid-19 cases, researchers said on Thursday, although a lack of data details stirred calls for more transparency.

The trial results, closely watched by developing countries counting on the vaccine to begin mass inoculations to help end a raging pandemic, was below preliminary findings from Turkish researchers and lacked detailed data provided on US and European vaccines...