COVID-19 Infectious Window and Transmission

Introduction to COVID-19 Infectiousness

The infectious window for COVID-19 typically begins 1-2 days before symptom onset and extends for a median of 5 days after symptom onset in mild-to-moderate cases, though two-thirds of patients remain infectious at day 5 and nearly one-quarter remain infectious at day 7 post-symptom onset 1, 2
Viral shedding begins 1-2 days before symptoms appear, making pre-symptomatic transmission a critical feature of COVID-19 spread 1, 2
This pre-symptomatic transmission capability distinguishes COVID-19 and contributes to its rapid pandemic spread 3

Viral titers peak in the early phase of infection, typically within the first 7 days of illness 1, 2, 4
Live virus remains detectable in the respiratory tract for up to 9 days in most individuals 4
Approximately 30-60% of patients shedding virus may have no symptoms, making asymptomatic transmission a significant concern 1, 2

Viral shedding continues for 1-2 weeks in mild-moderate cases 1, 2
The Centers for Disease Control and Prevention (CDC) suggests contagiousness typically lasts an average of 10 days from symptom onset 5
Viral shedding extends beyond 2 weeks in severe cases 1, 2
For immunocompromised patients or those with severe/critical COVID-19, contagiousness can extend up to 15 days 5
Viral viability has been documented up to 20 days from symptom onset in some cases 5

The incubation period ranges from 1 to 14 days, with a median of 5.1 days 3
Symptoms usually appear between 2 and 14 days after exposure 1, 2
Prolonged shedding of viral RNA has been observed in immunocompromised patients, indicating quarantine should extend to at least 20 or more days following symptom onset 6

For symptomatic patients, isolation should continue until at least 3 days have passed since recovery 5
Individuals with persistent symptoms beyond day 7 and positive testing should continue isolation, as this combination indicates active infection and potential infectiousness 5
Immunocompromised patients require extended isolation of at least 20 days following symptom onset 6