COVID-19 | A Covid-19 vaccine developed by China's Sinovac Biotech is 91.25 percent effective, according to interim data from a late-stage trial in Turkey, a potentially much better result than reported from a separate trial of the vaccine in Brazil.

Researchers in Brazil, which is also running a final Phase III trial of the vaccine, said on Wednesday the shot was more than 50 percent effective, but withheld full results at the company's request, raising questions about transparency...