Modelling the Delta Covid-19 Wave in Mumbai

Using agent based simulator (ABS), we attempt to explain the infectiousness of the delta variant through scenario analysis to best match the observed fatality data in Mumbai, where the variant initially spread. Our somewhat prescient conclusion, based on analysis conducted in March-April 2021 was that the new variant was 2-2.5 times more infectious than the original Wuhan variant. We also observed then that certain performance measures such as timings of peaks and troughs were quite robust to the variations in model parameters and hence can be reliably projected even in presence of model uncertainties. Furthermore, we introduce enhancements to help model variants, vaccinations, basic and effective reproduction number in ABS. Our analysis suggests an interesting observation - although slums have around half of Mumbai population and are much more dense and have higher prevalence, the effective reproduction number between slums and non-slums equalises early on and largely moves together thereafter.