Scientists at the Tata Institute of Fundamental Research (TIFR) jointly with a team at Indian Institute of Science (IISc) have developed a simulation model for the city of Mumbai to analyse the rate of infection spread of Covid-19.<br />'' <br />''Their model projects that Mumbai will approach herd immunity by December 2020 and January 2021. The TIFR scientists believe that after January-February 2021 there will be a substantial decline in cases of Covid 19.<br />'' <br />'' <br />''The mathematical projection on the ongoing Covid 19 worked out by TIFR scientists says that the simulation model gives a fairly accurate idea about the spread of the disease. Dr. Sandeep Juneja from the computer science department of TIFR told AIR that the fatalities rate which saw a peak in the month of June and July in Mumbai has been coming down since.<br />''<span style="font-style: italic; text-decoration: underline;"> </span><br />''He says by December or January large number of people in Mumbai would have been infected.<span style="font-style: italic; text-decoration: underline;"> </span>Dr. Juneja also says that there won't be much cases reported in January-February 2021 and thereafter, suggesting that the city population has achieved herd immunity.<br />''<span style="font-style: italic; text-decoration: underline;"> </span><br />''It will be a stage where by and large people would have got infected. He says, even now  close to 50 percent of Mumbai is infected. By January next year, around 50% people living in residential areas and 75 percent in slums would be infected.<br />''<span style="font-style: italic; text-decoration: underline;"> </span><br />''Dr. Juneja however says that there is a caveat to it as the scientists currently believe that re-infection will remain rare. If that changes then the projections will no longer hold the ground, he said.<br />