When Americans think of vaccines, they usually think Pfizer, Moderna or Johnson and Johnson — all American companies. But in much of the world, the jabs going into peoples’ arms will be made in China. Most come from a firm called Sinovac in Beijing. China’s government has spread more than a billion Sinovac doses around the world — and often for free. But there is a growing sense among some that this vaccine is not up to snuff — especially in China’s backyard, across Southeast Asia. Patrick Winn has the story.