The chance of infection of a secondary close contact depends on whether the close contact is infected or not. If the close contact is infected, the chance of infection is higher, and if the close contact is not infected, the chance of infection is lower.
A secondary close contact is a close contact of a close contact, and his or her infection is necessarily linked to the close contact. If the close contact is eventually diagnosed as a patient, then the secondary close contact has a higher chance of being infected, and if the close contact is not diagnosed, then the secondary close contact has a lower chance of being infected.
In addition, whether or not a secondary close contact is infected depends on a number of factors, including the speed of transmission of the pathogen and the degree of contact with the close contact. However, regardless of whether they are infected or not, secondary close contacts should be isolated according to local policies to prevent further spread of the pathogen.