On April 14, Kerala reported nine new cases of COVID-19. Out of this, five persons who tested positive for SARS-CoV-2 virus had international travel history. The positive test results come 23 days after international flights in India were barred since March 22, and 21 days since domestic flights were also stopped from March 24.
If a person could still test positive for the virus 20 days after being under quarantine, it raises new questions on the incubation period – the time between being infected and the symptoms of the disease showing up on your body. Over the past few days, Kerala has had cases of foreign returnees testing positive everyday, much after the 14-day period. In another case, a Kannur man who returned from Dubai on March 17, tested positive on April 12, exactly 26 days later.
The World Health Organisation (WHO) says in its Q and A section, “Most estimates of the incubation period for COVID-19 range from 1-14 days, most commonly around five days.”
However, it also adds: “These estimates will be updated as more data become available.”
Dr Amar Fettle, state nodal office for coronavirus in Kerala, makes similar observations. “The usual incubation period is 4 to 7 days. After the test, it is 0 to 14 days. However, there is something called double incubation period and for security reasons, this is the number that we have been following in Kerala. That is 28 days.”
He adds that what we are seeing is a novel virus, not one that’s been studied extensively. “It only has three or four months of history. It is too early to say concretely that the incubation period is 14 days. It is not yet time. So we go by what was known as the usual time – 14 days, and then we double it so that outliers are also covered. In 98 per cent of the cases, the symptoms start to show in 4 to 7 days, in one per cent this may take up to 14 days. The remaining one per cent covers the outliers. There is no mathematical rule in biological science. It is based on observation. It doesn’t mean a living organism can confine to that (set period of time).
On Tuesday, Kerala reported 386 cases in total, with 173 people under treatment and 211 having recovered. There have been two COVID-19 deaths in the state.