  The second wave of Covid-19 that started in mid-February 2021 in Mumbai is
now subsiding. Increasingly the focus amongst the policy makers and general
public is on the potential third wave. Due to uncertainties regarding emergence
of new variants and reinfections, instead of projecting our best guess
scenario, in this report we conduct an extensive scenario analysis for Mumbai
and track peak fatalities in the coming months in each of these scenarios. Our
key conclusions are - As per our model, about 80% of Mumbai population has been
exposed to Covid-19 by June 1, 2021. Under the assumption that all who are
exposed have immunity against further infection, it is unlikely that Mumbai
would see a large third wave. It is the reinfections that may lead to a large
wave. Reinfections could occur because of declining antibodies amongst the
infected as well as by variants that can break through the immunity provided by
prior infections. Even under a reasonably pessimistic scenario we observe the
resulting peak to be no larger than that under the second wave. We further
observe that under the scenario where the reinfections are mild so that they
affect the fatality figures negligibly, where the new variants (beyond the
existing delta variant) have a mild impact, as the city opens up, we observe a
small wave in the coming months. However, if by then the vaccine coverage is
extensive, this wave will be barely noticeable. We also plot $R_t$, the
infection growth rate at time $t$, and highlight some interesting observations.
