Covid-19 transmission period
Pro Research Analysisby 
Searched over 200M research papers
COVID-19 Transmission Period: Incubation, Latency, and Infectiousness
Incubation Period and Latency Period of COVID-19
Research consistently estimates the mean incubation period of COVID-19—the time from infection to symptom onset—at around 5 to 8 days, with most studies reporting a median between 5 and 7 days, and some cases extending beyond 14 days 1358. The latent period, which is the time from infection to when a person becomes infectious, is estimated to be about 3.3 days on average, indicating that individuals can become infectious before showing symptoms 39.
Serial Interval and Generation Interval
The serial interval, which is the time between symptom onset in a primary case and a secondary case, is generally found to be 4 to 5 days, often shorter than the incubation period 567. The generation interval, the time between infection events in a transmission chain, is estimated at about 6.7 days . These findings suggest that transmission can occur before symptoms appear.
Pre-symptomatic and Asymptomatic Transmission
A significant proportion of COVID-19 transmission occurs before symptom onset. Studies estimate that 37% to 50% of secondary infections are due to pre-symptomatic transmission, with some clusters showing even higher rates 2345+3 MORE. This means people can spread the virus even when they feel healthy or before they realize they are sick.
Infectious Period and Super-Spreading Events
The infectious period can begin a few days before symptoms and continues for several days after. The number of close contacts during the incubation period, especially just before hospitalization, can lead to super-spreading events, emphasizing the importance of early isolation and preventive measures 17. In familial and social clusters, rapid transmission has been observed during the late incubation period, even when the index case was asymptomatic 710.
Implications for Public Health Measures
Because a large portion of transmission happens before symptoms, relying solely on symptom-based interventions may be insufficient. Effective control requires measures such as social distancing, mask-wearing, and isolation of both symptomatic and asymptomatic individuals, as well as robust contact tracing and quarantine protocols 1348.
Conclusion
COVID-19 can be transmitted during the incubation and latent periods, often before symptoms appear. The average incubation period is about 5–8 days, with infectiousness starting as early as 3 days after infection. Pre-symptomatic and asymptomatic transmission play a major role in the spread of the virus, making early and comprehensive public health interventions essential for controlling outbreaks.
Sources and full results
Most relevant research papers on this topic
Characterizing COVID-19 Transmission: Incubation Period, Reproduction Rate, and Multiple-Generation Spreading
COVID-19 incubation period is 7.83 days, transmission rate from close contact is 0.13, and multiple-generation spread is 90%, suggesting prevention measures like social distancing and masks are crucial.
DOI