If quarantining not effective, can be 1.5-10 million; nationwide lockdown instituted now can help reduce impact.
An ICMR study for corona impact in Delhi suggests that, in a best-case scenario, infections in the city can cross 2 lakh. And the worst-case scenario, of 10 million, suggests the numbers put out by Ramanan Laxminarayan, of the US-based Center for Disease Dynamics, Economics and Policy are not as outlandish as many have made out to be; Laxminarayan had estimated that 1 million people could eventually die in India while the number getting infected could be over 300 million. This study was done before India initiated a nationwide lockdown.
The ICMR study, to be part of a special edition of the Indian Journal of Medical Research, chose Delhi along with Mumbai, Bengaluru and Kolkata as these are the big entry points for those coming from countries that are badly impacted by Corona.
ICMR has two models, an optimistic and a pessimistic one. In the optimistic one, one infected person infects 1.5 persons while in the pessimistic model, the infection is passed on to four people. The peak infection comes 200 days after the onset in February in the optimistic scenario and within 50 days in the pessimistic scenario. In the optimistic scenario, the peak infected are 1.5 million and this rises to 10 million in the pessimistic scenario.
Researchers from ICMR and Imperial College, London, arrived at the projections, based on their mathematical modelling to study the feasibility of limiting local infections through screening of travellers from countries with Covid-19 and the extent to which Covid-19 could be limited by quarantining.
If, however, Delhi and central governments are able to take adequate action like quarantining, things can be quite different. The optimistic scenario for Delhi changes sharply, if an intervention in which 50% of the infected are quarantined within three days of exhibiting symptoms—the total infections fall to 200,000, that too with the peak coming somewhere around 700 days from February.
For Mumbai, the optimistic scenario, with and without intervention, is 100,000 and 600,000, respectively. It is just under 100,000 and 500,000 for Kolkata, and under 100,000 and 300,000 for Bengaluru.