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Q: How long does it take for symptoms to start after I am exposed to COVID-19?

A: According to researchers at the Johns Hopkins Bloomberg School of Public Health, 97.5% of people will develop symptoms within 11.5 days of exposure. That means that the recommended 14-day quarantine period is a reasonable amount of time to monitor individuals for development of the disease.

Researchers reported the median incubation period of COVID-19 from exposure to the onset of symptoms is 5.1 days. The researchers estimated that for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine.

Study senior author Justin Lessler said, "Based on our analysis of publicly available data, the current recommendation of 14 days for active monitoring or quarantine is reasonable, although with that period some cases would be missed over the long term."

The report said that an accurate estimate of the disease incubation period for a new virus makes it easier for epidemiologists to gauge the likely dynamics of the outbreak. It also allows public-health officials to design effective quarantine and other control measures. Quarantines typically slow and may ultimately stop the spread of infection, even if there are some outlier cases with incubation periods that exceed the quarantine period.

Of course, COVID-19 is a new virus and researchers are learning more about it every day. We still face a significant challenge from people who have the virus but have no symptoms. The safest strategy continues to be wearing a mask and assuming you and others you are near could be asymptomatic carriers.

The findings were published online in the journal Annals of Internal Medicine.

— Jay Sizemore, M.D., Erlanger Health System and Cempa Community Care; member, Chattanooga-Hamilton County Medical Society

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Contributed Photo / Dr. Jay Sizemore
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