According to the Hong Kong researchers, the first time the patient got sick, he felt ill: He had a cough, a sore throat, fever, and headache, and had to be hospitalized. The second time the patient tested positive for the virus — four and a half months later — after being screened at the airport, he felt no symptoms at all. As virologist and physician Muge Cevik explains on Twitter, this is “in a way reassuring.” It’s what you’d hope to see the second time someone is infected with a virus: a less severe reaction. Which is all to say: You can be reinfected with the virus but still have some protective immunity to it. Why? There are many, many components of our immune system that are working together to fight the virus. And immunity doesn’t mean one single thing.