Coronavirus disease (COVID-19) in India till 9th April 2020
I have traced back (reverse modeling) reproduction number from the observed number of cases on different dates. This gives a multiplier of 1.5 in 5 days (cases multiply by 1.5 in 5 days - the minimum infectious period) from 30th January 2020 to 29th February 2020, increased to 2.5 from 1st of March (when cases showed sudden rise and social distancing was effectively implemented). A fortnight later, beginning 15th of March, the multiplier reduced to 2.1. THUS SOCIAL DISTANCING ITSELF WAS ABLE TO CUT TRANSMISSION RATE BY ABOUT 20%.
Lockdown effectively started on 23rd March with a call for Janta Curfew. The multiplier was expected to reduce to 1.25 after 15 days (from 7th of April) if properly implemented but Tablighi gathering substantially disrupted this pattern for a week, and increased the number of cases. The multiplier settled to 1.8 in the second week of April and is poised to come down further. Note, however, this is a multiplier and the cases once increased will continue to have impact on the numbers for times to come.
it would be interesting to find how the anticipated numbers differ from the soft lockdown (no gathering of 5 or more anywhere including transport, schools and effective social distancing but offices, markets and factories open with screening and alternative attendance) and hard lockdown as is from 25th of March 2020.