The average incubation period for the disease COVID-19, caused by the novel coronavirus named SARS-CoV-2, is 5.1 days with symptoms developing within 11.5 days for 97.5% of those infected. It has been confirmed by a new study coming from Johns Hopkins Bloomberg School of Public Health that examined 181 confirmed cases of COVID-19. This means that the 14 days of active monitoring (quarantine) is reasonable. The findings were published in the journal Annals of Internal Medicine.
A disease’s incubation period is the time between initial exposure to a pathogenic organism and the emergence of symptoms in a host. Knowing the period is essential to controlling the spread of the virus, but it can be complicated because they vary depending on the disease. For instance, measles has an incubation period of between nine to twelve days, but influenza incubates in only one to three days.
The researchers caution that the results of their study do not mean that someone is evident after five days. It merely validates the current two-week quarantine time-frame as an appropriate stretch for self-isolation following suspected exposure. Within that time, most people will have experienced symptoms. However, a small minority may have more extended incubation periods than 14 days.
Justin Lessler, senior author on the new study, explained:
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 researchers estimate in the study that for every 10,000 subjects infected, about 101 would develop symptoms after two weeks. Therefore, it is suggested that for ultra-high-risk instances, active monitoring be extended past the 14 days — for example, healthcare workers who were exposed to the virus and weren’t wearing protective equipment.
The social and economic costs of quarantine have also been weighed against the consequences of failing to identify asymptomatic cases. Jonathan Ball, a University of Nottingham professor of molecular virology, who did not work on this new study, said:
While the study suggests that in some people the incubation period might be longer, we have to acknowledge that the models they 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 might not be true – the real infection timepoint might be much later, yet assuming the infection occurred at an earlier date will make the incubation period appear longer.
As it stands, there is little evidence to suggest that a quarantine or self-isolation 14 days are not suitable. Also, there is little if any evidence that people can routinely transmit the virus during the asymptomatic period.
Another important thing to note is that the disease is often most transmissible during the symptomatic stage – like when a person is coughing. During a disease’s incubation period, the person may or may not be contagious. Right before the incubation period is a phase called the latent period – which is the time from initial exposure to infectiousness. It is still unclear exactly when a person with COVID-19 becomes infectious or how contagious they are during the asymptomatic incubation stage.
