There is scientific basis and epidemiological significance for the 21-day lockdown period announced by PM Modi.

Is there any public health/epidemiological significance to the 21-day lockdown period announced by Prime Minister Narendra Modi?

It seems that rich scientific data has fed this decision to announce a 21-day lockdown period. In fact, 21-day quarantines have been discussed elaborately in the context of Ebola and the calculations are based on the estimated incubation period of the virus in a human host. The 21-day quarantine value is derived from interpretations of outbreak data, past and present, public health experts said.

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Median incubation period

“In epidemiological terms, the logic is that we have arrived at an incubation period of 14 days. Give another week for the residual infection to die out, for the tail end, to be entirely safe, and you arrive at 21 days,” says Tamil Nadu’s Director of Public Health K. Kolandasamy. This being a new coronavirus, they have estimated that the median incubation period (the time between the entry of virus to the onset of symptoms/ disease) falls within this period.

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Science Daily recently reported of a new study in the journal Annals of Internal Medicine “that calculates that the median incubation period for COVID-19 is just over five days and that 97.5% of people who develop symptoms will do so within 11.5 days of infection. Researchers headed by Nicholas Reich, Associate Professor in the School of Public Health and Home Sciences, University of Massachusetts, Amherst, reportedly examined 181 confirmed cases with identifiable exposure and symptom onset windows to estimate the incubation period of COVID-19. They conclude that ‘the current period of active monitoring recommended by the U.S. Centers for Disease Control and Prevention [14 days] is well supported by the evidence’.”

Most accurate models

Prof. Reich, it said, heads a flu forecasting collaborative that has produced some of the world’s most accurate models in recent years.

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This is the most effective way of preventing the spread of the infection from those already infected into the community, K. Kuganantham, a public health expert based in Chennai, explained. “In fact, for infections that are transmitted in this manner, this is the one thing to prevent the rapid spread of infection within the community.” That, and maintaining personal hygiene and practising personal distancing, he added.

Breathing space

Dr. Kolandasamy further explained that in the interim, the lockdown or quarantine also creates some breathing space — to convince people of the seriousness of the situation and build positive public opinion, carry out disinfection of all buildings, vehicles and surfaces, and allows hospitals to prepare themselves for the next phase of operations. “We cannot stay at home indefinitely, but we must make our sacrifice count, so people need to follow these instructions strictly, as if their life depended on it. It does, you know,” he said.