Bengaluru and Mumbai are likely to have a second wave of Covid-19 infections after the lockdown is lifted on May 3 unless measures are taken to aggressively trace, localise and isolate Covid-19 cases.

This grim forecast has been made in a working paper by 18 scientists from the Indian Institute of Science (IISc) and the Tata Institute of Fundamental Research, Mumbai, using a mathematical, city-based epidemic simulator.

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Several adjustable parameters, such as disease progression parameters, plus daily contact rate are set. The settings can then be run through a filter of 11 different “intervention” settings, including no government intervention to an infinite lockdown, a lockdown for 25 days and a lockdown for 40 days (which mirrors the present situation).

The “interventions” are modelled as beginning on March 25, the day of the nationwide lockdown. Data on a log scale shows that if there is no intervention at all, the number of fatalities in the city would be about 28 by May 1. By June 1, however, the modelling shows that if the lockdown is not continued, the number of deaths could reach 23 by July 1, before climbing to 33 by August 1.

According to data from the state Department of Health and Family Welfare, there have been four recorded deaths in the city so far. Scientists said these number projections do not take into account aggressive contact tracing, testing, and isolation which can change the course of the epidemic.

Professor Rajesh Sundaresan of the Department of Electrical Communication Engineering, IISc, the corresponding author for the paper, explained that the model is agent-based and uses a fine-grained mathematical replica of a city, mimicking various interaction spaces such as households, schools and workplaces.

“If there are 10 million people in Bengaluru, the city’s model also has that many individuals,” he said, adding that the model also takes into account population densities, age distribution, household size distribution, commute distances and several other

parameters.

In their model, the researchers ‘seeded’ infections in the simulated cities and tested how the epidemic would spread under different scenarios when restrictions are phased out.

In all of these, the researchers assumed that cases would continue to be isolated with 90 percent compliance.