Among about 300 coronavirus vaccine candidates being developed around the world, at least nine were undergoing phase 3 human trials as of September 28, 2020, according to the World Health Organization. Of the nine vaccines at that stage of research, four are being produced in China, making the country one of the world’s front-runners in the development of Covid-19 vaccines. Beijing’s claim that China is close to mass production of a vaccine has raised questions about the efficacy of the shots,…