A recent study published in the reputed peer-reviewed medical journal, Annals of Medicine, has said that, on an average, the first COVID-19 symptoms will appear in an infected person in five days. At any rate, it won't take more than 12 days for the first symptoms - cold or sore throat - to rear its head in most of the cases.
The study says that 97.5 per cent of those who develop symptoms will do so within 11.5 days of infection. Yet, very rarely the incubation period (time between exposure to the virus and first symptoms) can be longer. “These estimates imply that, under conservative assumptions, 101 out of every 10 000 cases will develop symptoms after 14 days of active monitoring or quarantine,” the study says.
Kerala's insistence on 28 days quarantine, therefore, makes sense.
A scary prognosis is, the infected person can pass on the virus to another before symptoms start to show.
Here is what the Annals of Medicine study says: “We note that time from exposure to onset of infectiousness (latent period) may be shorter than the incubation period, with important implications for transmission dynamics.”
In other words, an asymptomatic person can also spread the disease. Note that the Pathanamthitta-based Italy returnees had claimed they had no symptoms when they landed in Kochi.
The Annals of Medicine findings were based on the study of confirmed COVID-19 cases reported between January 4 and February 24, mostly in China. The study was done to estimate the length of the incubation period of COVID-19 and describe its public health symptoms.
In December 2019, a cluster of severe pneumonia cases of unknown cause was reported in Wuhan, Hubei province, China. The initial cluster was linked to a seafood wholesale market in Wuhan, although many of the initial 41 cases were later reported to have no known exposure to the market.
A novel strain of coronavirus belonging to the same family of viruses that cause severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), as well as the four human coronaviruses associated with the common cold, was subsequently isolated from lower respiratory tract samples of four cases on January 7, 2020.
On January 30, the World Health Organization declared that the COVID-19 outbreak constituted a Public Health Emergency of International Concern, and by February 28, more than 80,000 confirmed cases had been reported.
At this moment, there are over 1,10,000 confirmed cases and over 4000 deaths across the world.