More than three months into the coronavirus pandemic, health-care workers on the front-lines of the battle against Covid-19 say they still face shortages of personal protective equipment. The personal protective shortage was one of the early flashpoint of the coronavirus pandemic. Masks, ventilators, face-shields. It seemed nearly every kind of personal protective equipment was hard to find when Covid-19 first ripped through epicenters like New York City. Here’s how the medical device supply chain works—and how it failed when it was needed most.