The incubation period of a pathogen/disease describes the duration between initial exposure and the onset of disease symptoms. In the case of coronavirus, the incubation period is estimated to be 5 – 6 days; however, the exact recommended range is 1 - 14 days.
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What is coronavirus?
Coronaviruses are a group of viruses that cause infection in animals and humans. In humans, coronaviruses cause a variety of respiratory infections, ranging from a mild common cold to more severe Middle East Respiratory Syndrome (MERS), Severe Acute Respiratory Syndrome (SARS), and recently evolved coronavirus disease 2019 (COVID-19). The coronavirus responsible for COVID-19 is named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
What is an incubation period?
An incubation period, which measures the time from pathogen exposure to disease onset, provides valuable information about disease transmission dynamics, as well as facilitates the implementation of appropriate non-pharmaceutical control measures, such as contact tracing and estimating the duration of home quarantine for people who are infected by the pathogen or came in contact to an infected person.
Moreover, the incubation period can help health professionals effectively diagnose a disease based on observed symptoms and the patient’s clinical history.
There are several determining factors for the incubation period, including the route of pathogen transmission, pathogen load (amount of pathogen entered the body), and functionality of the host immune system.
The most reliable way of estimating the incubation period is to methodically study case reports that involve patients with single pathogen exposure. In the case of patients who are exposed to the pathogen multiple times, it is impossible to determine which exposure triggered the disease onset.
What is the incubation period of SARS-CoV-2?
Since its emergence in December 2019 in China, the very rapid spread of deadly SARS-CoV-2 has warned the need for searching epidemiological characteristics of the virus, including the incubation period.
According to the World Health Organization and the Centers for Disease Control and Prevention, the estimated range of incubation periods of SARS-CoV-2 was 1 – 14 days. However, the exact incubation period was estimated to be 5 – 6 days.
A recent study analyzing confirmed cases of COVID-19 (January 2020 – February 2020) obtained from 50 provinces, regions, and countries outside Wuhan, China (a total of 181 cases), has estimated that the average incubation period of SARS-CoV-2 is 5.1 days. About 97.5% of COVID-19 patients are estimated to develop symptoms within 11.5 days of infection, and about 2.5% of patients are estimated to develop symptoms within 2.2 days.
Regarding specific symptoms, the study findings reveal that the average incubation period to fever onset is 5.7 days. The study has also assumed that out of 10,000 confirmed cases, 101 will develop symptoms after 14 days of isolation.
One important thing to be remembered is that the incubation period may vary from person to person. One study analyzing 1099 confirmed COVID-19 patients has shown that the average incubation period is estimated to be 3 days, with an incubation period range of 0 to 24 days. There is also evidence claiming that the incubation period can be extended up to 27 days. Regarding asymptomatic cases, there is one evidence claiming that the incubation period for an asymptomatic patient is 19 days.
Regarding an incubation period of as long as 24 days, the World Health Organization mentioned in a press release that such a long incubation period is more likely due to a second infection rather than a continuation of the first infection.
What are the incubation periods of other respiratory viruses?
According to scientific evidence, the estimated incubation period of SARS CoV is 5 to 7 days, which can be extended up to 10 days. In the case of MERS CoV, the average incubation period is 5 days; however, the incubation period may vary from 2 to 14 days.
In the case of seasonal influenza, the average incubation period is 2 days, with a range of 1 to 4 days. In the case of swine flu (H1N1 influenza virus), the incubation period varies between 1 and 4 days, which can be extended up to 7 days.
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