In the past, working in a language school, I have heard people talking about the teachers being the ones who are on the front line. It's quite dramatic language, especially in the light of this coronavirus situation and the fact that health workers are facing much, much tougher conditions. At the moment, this phrase is being used a lot for those people who are working in hospitals. In fact, these are the real heroes of the moment. It's the health workers working on the frontline.