The contagious period for COVID-19 generally lasts about 10 days for people with mild to moderate illness. Most individuals are contagious starting 1-2 days before symptoms appear and remain so for about 5-10 days after symptom onset

. For severe cases or people with compromised immune systems, the contagious period can extend to 20 days or longer

. Asymptomatic individuals can also spread the virus, though their contagious period may be shorter and their infectivity somewhat weaker

. It is important to note that a positive PCR test may detect viral RNA for weeks after recovery but does not necessarily indicate contagiousness, whereas rapid antigen tests are more indicative of active contagious infection

. In summary:

• Mild to moderate cases: contagious roughly 5-10 days after symptoms begin.
• Severe or immunocompromised cases: contagious up to 20 days or more.
• Contagiousness starts about 1-2 days before symptoms.
• Asymptomatic carriers can be contagious but possibly for a shorter duration.

These timelines help guide isolation and public health measures to prevent spread