Right now, there is no test to decode when COVID-19 stops being contagious.
In the absence of this, doctors and medical professionals are only basing a person’s COVID status, by evaluating their symptoms. If a person sees a reduction of other symptoms, he or she is declared fit enough to mingle around society (of course, by continuing to follow sanitation and precautionary measures).
According to CDC guidelines, the following set of criterion need to be met before a person can be declared fit to exit his quarantine/isolation
-A person goes three days without having a fever (and does not use fever reducers)
-Sees a reduction in symptoms
-It has been over 10 days since the symptoms started to show up.
For a person with compromised immunity, the self-isolation period is usually extended upto 20 days.