Covid-19 has an incubation period of 5.1 days, says study

TV Jayan New Delhi | Updated on March 11, 2020

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Data-backed research confirms 14-day quarantines are adequate to contain the spread of the disease

Much to the relief of public health experts and governments all over the world battling the coronovirus (Covid-19) outbreak, a team of researchers has found that the infection has an estimated incubation period of 5.1 days, and the current practice of 14 days of quarantine is therefore good enough to contain its spread.

For the study, which appeared in the journal Annals of Internal Medicine on Monday, researchers at Johns Hopkins Bloomberg School of Public Health analysed publicly available data on 181 cases from China and other countries that were detected prior to February 24.

The new study does not vastly change the incubation period estimate vis-à-vis the earlier ones, but it has better backing of data.

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, and 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.

Development of symptoms

The analysis carried out by a team led by Justin Lessler, an epidemiologist with the Bloomberg School, suggested that about 97.5 per cent of people who develop symptoms of Covid-19 will do so within 11.5 days of exposure. The researchers estimated that for every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine.

More importantly, this median time from exposure to onset of symptoms suggests that the 14-day quarantine practised by most public health agencies around the world currently is reasonable enough to contain the infection. During the quarantine period, individuals who are known to be at high risk of infection due to contact with known cases or travel to a heavily affected areas are actively monitored for known symptoms.

“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,” said Lessler in a statement.


Quick spread

But that said, it is not that there is no reason to worry. According to Tanja Stadler, a mathematician studying computational evolution at the Swiss Federal Institute of Technology in Basel, the so-called reproduction number of the Covid-19 infection is between 2 and 3.5. Reproduction number indicates the number of people infected on an average by an infected person. If the number of reproductions is greater than one, the epidemic spreads exponentially.

“The corona epidemic is spreading much faster. This shows that very far-reaching health policy measures have to be taken to keep the number of reproductions below one. Only then will the epidemic go away,” Stadler said in an interview with Swiss-German daily Tages-Anzeiger on Tuesday.

The global outbreak of Covid-19 began in December 2019 in Wuhan, a city of 11 million in central China. It has so far resulted in 1,15,800 officially confirmed cases around the world and over 4,200 deaths from pneumonia caused by the virus, per the latest updates. The majority of the cases are from Wuhan and the surrounding Hubei province, although dozens of other countries have been affected, including the US, South Korea, Iran and Italy. About 60 million residents of Italy are under a complete lockdown.

The incubation period for SARS-CoV-2 is in the same range as SARS-CoV, a different human-infecting coronavirus that caused a major outbreak centred in southern China and Hong Kong in 2002-04. On the other hand, MERS-CoV, a coronavirus that has caused hundreds of cases in West Asia since 2012, with a relatively high fatality rate, has an estimated mean incubation period of 5-7 days.

Published on March 11, 2020

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