Covid-19 infectious period
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COVID-19 Infectious Period: Key Findings
Infectious Period Duration in Symptomatic and Asymptomatic Cases
Research shows that the infectious period of COVID-19 varies depending on whether a person is symptomatic or asymptomatic. For asymptomatic cases, the median infectious period is estimated to be about 6.5 to 9.5 days. For symptomatic cases, the mean time from symptom onset to two negative RT-PCR tests is around 13.4 days, with the potential maximal infectious period (from symptom onset to hospital discharge or death) averaging 18.1 days. However, these durations can be shorter in children or less severe cases. The presymptomatic infectious period typically ranges from less than 1 day to 4 days, indicating that people can spread the virus before showing symptoms .
Infectious Period Estimates from Modeling Studies
Mathematical and statistical models provide a range of estimates for the infectious period. The median infectious period reported in a systematic review of models is about 9.94 days, with an interquartile range of 3.93 to 13.50 days . Another modeling study found a longer infectious period, averaging 17.82 ± 2.95 days, suggesting that the duration can be quite variable depending on the data and methods used . Most models set the infectious period between 2.3 and 10 days, but some studies suggest it could be longer, especially in the absence of interventions .
Unmitigated Infectiousness and Transmission
When looking at the unmitigated profile of COVID-19 infectiousness (i.e., before widespread interventions), about 19% of transmissions may occur 14 days or more after infection, which is higher than previously thought. This finding highlights the potential for prolonged infectiousness in some individuals and the importance of considering longer isolation periods in certain cases .
Incubation Period and Serial Interval
The incubation period—the time from exposure to symptom onset—has a median of about 5 to 5.9 days, with most people developing symptoms within 11.5 days of infection Men2020Lauer2020. The serial interval, which is the time between symptom onset in a primary case and a secondary case, is estimated to be around 4 to 4.6 days. This short serial interval suggests that a significant portion of transmission can occur before symptoms appear, making early detection and isolation challenging .
Latency and Pre-symptomatic Transmission
The latency period, or the time before an infected person becomes infectious, is often assumed to be similar to the incubation period in many models. Some studies also account for pre-symptomatic transmission, which can lead to overestimation of the basic reproduction number (R0) if not properly adjusted Xiang2021Liu2020.
Conclusion
The infectious period for COVID-19 is variable but generally ranges from about 6 to 18 days, depending on symptom status and severity. A significant portion of transmission can occur before symptoms develop, and some individuals may remain infectious for longer than two weeks, especially in the absence of interventions. These findings underscore the importance of timely isolation, extended monitoring in some cases, and the need for flexible public health policies to effectively control the spread of COVID-19 Byrne2020Lin2020Peirlinck2020+3 MORE.
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