The antigen test is a test that finds an antigen using an antibody against the new coronavirus, and detects a protein fragment on the surface of the virus as a marker for infection.
Antigens can generally be detected in upper respiratory tract specimens during the acute phase after infection.
It can be used to determine new coronavirus infections along with PCR tests. Therefore, even if you develop symptoms that seem to be a new coronavirus infection, if this test is negative between the 2nd and 9th days of the onset, it means that you are not a new coronavirus infection at that time.