When people recover from an virus infection, their body is left with some memory of how to fight the virus when they encounter it again. The virus is antigens and recovered patient antibodies help fighting the virus.
This ability of the immune system to have a memory for previous antigens is the basis for vaccination. This immunity is not always long-lasting or totally efficient, however, and can decrease over time.
It is not known how long immunity might last after being infected.
Zhang Dingyu, director of the Jinjintan Hospital in Wuhan, said patients recovered from COVID-19 have a large number of comprehensive antibodies in their blood, which can fight the virus.