False-negative and false-positive antigen tests that are negative at 15 minutes and positive at 20 minutes may be due to improper testing, incorrect antigen testing, or recent vaccination against a new coronavirus. It is recommended to do several antigen tests to improve the accuracy or to perform nucleic acid test for clarification. 1. Improper operation: False positives can easily occur due to incorrect operation during the test, lack of instructions during the test, such as the sample being in a cold and damp place for a long time, which can easily lead to the sample being affected by the environment and microorganisms. 2. Antigen test detection error: due to the antigen test paper and the principle of the test leads to antigen test accuracy is low, after the test is prone to antigen test 15 minutes negative 20 minutes after the phenomenon of positive. 3. Recent vaccination with new coronavirus vaccine: recent vaccination with new coronavirus vaccine will survive the new coronavirus inactivation virus in the body, so in the process of antigen detection will make the result disturbed and false positive phenomenon. Nucleic acid testing is generally more accurate than antigen testing, and patients can apply for nucleic acid testing after reporting to the community.