As incubation period is 14 days, the cases emerging now are older and they have to be discounted.

The impact of the lockdown could be gauged only after two weeks, government as well as independent experts suggest.

On the evening of March 24, Prime Minister Narendra Modi announced a nationwide 21-day lockdown to arrest “community transmission” of the coronavirus. Between March 24 and April 1, the number of COVID-19 positive cases has more than doubled — from 606 on March 25 to 1,637 on April 1. This, however, was slower — about half the rate of growth from the week before when only 151 cases were confirmed on March 18.

Coronavirus | Interactive map of confirmed coronavirus cases in India

The growth in positive cases in India is slower than many countries that are dealing with the worst of the pandemic. On March 8, the United States recorded 541 cases in two days, and the figure nearly doubled to 994 cases. In the last week, however, it has increased 75%.

Indonesia, which as on March 31 had 1,528 cases — and therefore roughly in the league of India — is also following a similar growth rate. It had 686 cases on March 24 or a little less than half the cases from today. Though it has laws restricting movement, there is no lockdown.

Government experts as well as independent researchers concur that it is early to estimate the impact of the lockdown on slowing down the spread of the virus. “The incubation period of the virus is 14 days. Therefore, the cases we are seeing are older cases (from before March 24). So only once these old cases are discounted can we judge the impact of the lockdown. Whatever models and statisticians say, nobody can really predict the outcome of the epidemic,” Raman Gangakhedkar, ICMR’s chief scientist and spokesperson for COVID-19 communication, said at a press briefing.

Coronavirus | India sees a sharp spike in infections

Sujatha Rao, formerly Secretary of the Health Ministry, tweeted on Tuesday: “Impact of lock down can only be known after 5th April. Today’s infections are of the situation two weeks ago.” However both of these reflect the extreme outer limit of the incubation period — defined as the time taken to contract the virus and an infected person manifesting symptoms. The World Health Organization says incubation is commonly of 5 days, with 1-14 days being the range.

Coronavirus India lockdown Day 8 updates | Helpline numbers

Giridhar Babu, an epidemiologist and physician associated with the Public Health Foundation of India, said it would take a minimum of three weeks and a lockdown would be useful only with heightened testing, particularly to catch those who might be carrying the virus but were not yet manifesting symptoms. “Lockdown alone, without an increase in finding the new cases either through syndromic approach or increased rate of testing, is not enough to break the chain. Also reviewing of the States with silent areas [where very few cases are reported] is important as is contact-tracing of all those people who might have got the infection,” he said in an email.

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