Theoretically, there is a possibility of reinfection in patients with neocoronary pneumonia nine days after discharge from the hospital, but it is minimal and may be caused by the following reasons: 1. Although the patient has been cured and there are no symptoms from the outside, the virus may remain in the body, only in a small amount. Because the current nucleic acid of the new coronavirus is a qualitative test, not a quantitative test, so it is not detected; 2, the number of viruses in the patient’s body is not small, but due to errors or improper operation in the sampling, delivery or testing process, resulting in a false negative test. The nucleic acid detection technology currently used itself has a certain percentage of false-negative cases, with the possibility of systematic errors resulting.