I suspect they prevent the virus from running amok and the body's own immune system provides the 'cure'. Chloroquine seems to be used to suppress them immune system. One of the problems, ironically, with a CoV infection is that the body generates a massive immune response, which causes 'second order' problems. Chloroquine, the anti-malarial of choice here, seems to be used to attenuate that reaction. Strange, but clever.