If you find out you’ve been exposed to someone who’s tested positive for Covid-19, a rush of questions might come to mind: Do I have to quarantine? What if I can’t find a good mask or a test? Even if I test negative, can I be certain that I’m not contagious?

With omicron causing record-shattering case growth over the past few weeks, the Centers for Disease Control and Prevention’s (CDC) guidelines about what to do after exposure have shifted, and they remain frustratingly unclear. The last thing anyone wants to do when they’ve just learned...