A new study confirms previous estimates suggesting that the median incubation period for the new coronavirus, SARS-CoV-2, is about 5 days.
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All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.
One of the most frequently asked questions from members of the public since the start of the new coronavirus outbreak has been: What is the virus’s incubation period?
This refers to the period between contracting the virus and showing physical symptoms.
According to information from the World Health Organization (WHO), current estimates indicate that SARS-CoV-2 could take anywhere between 1–14 days to incubate. However, they suggest that the most common incubation period is about 5 days.
Now, a new study from Johns Hopkins Bloomberg School of Public Health in Baltimore, MD, confirms that the median incubation period of the new virus is around 5 days, meaning that about half of the people who contract SARS-CoV-2 will start showing symptoms at that point in time.
The researchers based their findings — featured in Annals of Internal Medicine — on the data of 181 individuals with confirmed COVID-19. Most of these people had been stationed in or traveled to and from Wuhan in China, the epicenter of the outbreak.
In confirmation of existing estimates, the current study also estimated that SARS-CoV-2’s median incubation period is 5.1 days.
While this means that half of the people with the virus will show symptoms within 5 days, for many others, it will take longer. Overall, 97.5% of people will show symptoms within the first 11.5 days.
“This work provides additional evidence for a median incubation period for COVID-19 of approximately 5 days, similar to SARS,” the investigators write in their study paper.
“Under conservative assumptions,” the researchers go on to state, only around 101 of every 10,000 people who contract SARS-CoV-2 are likely to develop symptoms after 14 days. This is the period that public health agencies, such as the Centers for Disease Control and Prevention (CDC), currently advise for self-quarantine.
“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.”
– Senior author Justin Lessler, Ph.D.
In commenting on the current findings, virologists point out that the study seems to confirm that current public health strategies — such as the 14-day quarantine — are correct.
However, they also caution that some of the assumptions made by the original researchers when they conducted their study may be incorrect.
For instance, Prof. Jonathan Ball, from the University of Nottingham in the United Kingdom notes that “we have to acknowledge that the models [the study authors] use to estimate incubation period make key assumptions, and perhaps the assumption most likely to impact on their data is that a person became infected as soon as they came into contact with the virus.”
“This,” he stresses, “might not be true — the real infection time point might be much later, yet assuming the infection occurred at an earlier date will make the incubation period appear longer.”
You can read Prof. Ball and other experts’ full comments here.
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