Incubation period: Evidences on SARS-CoV-2 (COVID-19)

New Delhi, April 04, 2020:

How long after the infection do symptoms appear? Are people infectious during this time?

What do we know?

• The best estimate of the incubation period of COVID-19 at present stands at 5.1 days, with 99% of individuals exhibiting symptoms within 14 days following exposure.Less than 2.5% of infected individuals exhibit symptoms sooner than 2 days following exposure. 
• The range of incubation periods is wide, with estimates of 24, 3,  and 18 days.
• COVID-19 test can be positive in individuals lacking clinical symptoms.
• Individuals can be infectious while they are asymptomatic.  Additionally, asymptomatic individuals can carry similar amounts of virus in their nose and throat as symptomatic individuals.
• While the infectious period is largely unknown, it could possibly be up to 10-14 days.
• Approximately 4 to 7.5 days are there, on an average, between symptom onset in successive cases of a single transmission chain.

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• A majority of individuals is admitted to the hospital within 8-14 days of symptom onset.
• Patients are positive for COVID-19 via PCR for 8-37 days following symptom onset.
• Individuals may test positive via PCR for 5-13 days after symptoms disappear and hospital discharge. The ability of these individuals to infect others is not clearly known.
• As per WHO, no evidence of re-infection with SARS-CoV-2 after recovery exists.
• Experimentally infected macaques could not be reinfected after their primary infection resolved.

 What do we need to know?

• The average infectious period during which individuals can transmit the disease?
• Are individuals infectious after hospital discharge and clinical recovery, or do positive PCR tests only detect non-infectious virus?
• Can individuals become re-infected after recovery? If yes, how long after?

-Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA

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