Can the antigen test detect the virus immediately after initial contact with a positive case?

Generally, immediately testing for antigens after initial contact with a positive case often fails to detect the virus. It may only be detected after waiting a certain period (e.g., 2–3 days) post-exposure, when the viral load reaches a detectable level. If concerned, it is recommended to seek medical advice early. Detailed analysis is as follows:

Right after exposure to a positive case, the virus has just entered the body and has not yet replicated significantly. The viral load is extremely low—far below the sensitivity threshold of antigen tests. At this stage, even if an antigen test is performed, it is unlikely to capture the viral signal, and the result will most likely be negative, making it impossible to accurately determine infection.

If testing is delayed by 2–3 days after exposure (longer in some cases), the virus may have completed initial replication in the body, increasing the viral load to a level detectable by antigen tests. Provided the individual's immune system does not clear the virus rapidly, the test may then return a positive result. However, the exact time to detection varies among individuals and depends on factors such as the amount of viral exposure and the strength of one’s immune system.

After contact with a positive case, it is recommended to wait 2–3 days before conducting an antigen test. During this period, individuals should monitor their health closely. If symptoms such as fever or cough develop, they should get tested promptly and take appropriate protective measures to prevent further transmission of the virus.