Chinese vaccines are poised to fill gap, but will they work?

With rich countries snapping up supplies of Covid-19 vaccines, some parts of the world may have to rely on Chinese-developed shots to try to conquer the outbreak. The question: Will they work? There is no outward reason to believe they won't, but China has a history of vaccine scandals, and its drugmakers have revealed little about their final human trials and the more than 1 million emergency-use inoculations they say have been carried out inside the country already.