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New study on COVID-19: It takes about 5 days from exposure to symptoms

The research also shows that most people develop symptoms within the span of 12 days with some displaying only mild signs

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A new medical study on the virus that causes the respiratory illness COVID-19 has shown that it takes an estimate of around 5.1 days for the median disease incubation period—from the time of exposure to showing symptoms. Understanding that timeline is extremely vital to the development and execution of effective disease containment and prevention measures.

With the world in the grip of the COVID-19 outbreak, scientists and experts are urgently looking for more insight into the virus behind the disease—how it behaves, who it targets, how long it takes for infected people to show symptoms and how severe it can potentially get.

The study, entitled “The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application”, was led by researchers at Johns Hopkins Bloomberg School of Public Health in the United States and published on Tuesday (Mar 10) in the online medical journal Annals of Internal Medicine. Its objectives were to estimate the length of the incubation period of COVID-19 and describe its public health implications.

The researchers conducted an analysis of publicly available data on infections from the new coronavirus, SARS-CoV-2, which causes the respiratory illness COVID-19. 

The study yielded an estimate of 5.1 days as the median time for the disease to incubate and begin displaying symptoms.

This median time from exposure to onset of symptoms suggests that it is largely harmonious and in accordance with earlier studies on the virus, which were published on Eurosurveillance, a European journal on infectious diseases, and in the US National Library of Medicine by the National Institute of Health.

All three studies support that the length of the 14-day quarantine period enforced by most governments and health bodies around the world is indeed reasonable.

The paper noted that the coronavirus’ median incubation period is 5.1 days,with most people developing symptoms within the span of 12 days.

In some cases, however, patients can display such mild symptoms, making the virus very difficult to detect.

Study co-author Justin Lessler, an associate professor of infectious disease epidemiology at the Johns Hopkins Bloomberg School of Public Health, said that incubation numbers will “inevitably be refined as we get more information”, adding that having foresight is crucial for “thinking about controls such as quarantine and active monitoring”.

The study’s authors analysed 181 confirmed COVID-19 cases reported by health organisations and media outlets between Jan 4 and Feb 24, with most of the cases being those who had travelled to Wuhan, China, the epicentre of the outbreak.

While it was difficult to figure out the exact point of infection for each case, the researchers carefully looked for and studied the specific sequence of events—such as an activity or interaction where the infection may have been passed. This allowed them to calculate the delay between exposure to the virus and the onset of symptoms.

Individuals suspected or confirmed to be infected with COVID-19 are usually isolated for a 14-day period, using a week-long average incubation period as a basis. It is the expectation that those infected with the virus will show symptoms within the 14 days of quarantine.
While that has been the case for most infected persons, there have been reports of incubation periods lasting longer than two weeks. Regarding this, the new study noted that an estimate of about one per cent out of every 10,000 patients could develop symptoms even after being discharged from the 14-day quarantine period.
This is a risk that governments and public health officials may have to contend with, said Lessler. At this stage in the COVID-19 outbreak, the possibility of stopping the disease entirely is no longer viable.
He suggested that, at this point, “some risk mitigation and slowing things down” could be a “better strategy” than ramping up quarantine measures, which are costly, particularly for health care workers.

While the new study’s results supports current proposals for the length of quarantine or active monitoring of persons potentially exposed to the SARS-CoV-2 virus the causes COVID-19, it acknowledges that “longer monitoring periods might be justified in extreme cases”.

With more data on the virus, such as the incubation period and mortality rates, medical professionals will be more equipped in this the fight against the COVID-19 outbreak. To date, the disease has currently claimed more than 4,300 lives and affected more than 121,000 persons in 121 countries and territories.


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