COVID-19, the novel coronavirus with apparent origins in Wuhan, China, has overtaken the world of emergency medicine. It’s so new that doctors can’t confidently assert much about it, except that it is highly contagious and potentially lethal. Its specific lethality, however, remains hotly contested—and difficult to prove, given low testing rates and the relatively high prevalence of asymptomatic carriers. You probably already know the basics. Here are five things you must understand to protect yourself and the people you serve.