As more and more people become infected with COVID-19, more and more people are also going to be reinfected. But there's another type of reinfection known as a rebound infection, which can happen in the days after you've recovered. The US President Joe Biden tested positive again this week for COVID-19 only a few days after he was cleared following his treatment with antiviral medication Paxlovid. So what could be going on? How common are rebound infections and could it extend to people who don't take the drugs also being reinfected?