Thread by @agrawalmanindra

<SUTRA's analysis of third wave> @stellensatz @Ashutos61 @Sandeep_1966 @shekhar_mande It took us a while to do the analysis for three reasons. First, loss of immunity in recovered population. Second, vaccination induced immunity. Each of these two need to be estimated for future.

And third, how to incorporate the two in the model. Fortunately, it turned out that both can be incorporated by suitably changing contact rate and reach parameters. So that takes care of third one. First two required detailed analysis.

We went through the studies done in the past on loss of immunity and used conservative numbers for them. Similarly, we looked at the projected vaccination rate over next few months, included the effects of vaccine-hesitancy, and arrived at month-wise estimates for vaccination.

Then came imponderables. Will there be a new, more infectious, mutant? If yes, when will it strike? When will people abandon caution completely as in March this year? One can only make guesses, which may be completely wrong. Hence, it is better to compute a few what-if scenarios.

We have created three scenarios. One is optimistic one. In this, we assume that life goes back to normal by August, and there is no new mutant. Second is intermediate one. In this we assume that vaccination is 20% less effective in addition to optimistic scenario assumptions.

Third is pessimistic one. This has one assumption different from intermediate one: a new, 25% more infectious mutant spreads in August (it is not delta+, which is not more infectious than delta).

Here are plots for the three scenarios. Blue curve is actual data. Orange one is model prediction until May. Dotted curves are three scenarios plotted from June.

There is hardly any difference between optimistic and intermediate scenarios suggesting vaccine efficacy changes do not have significant impact. A faster spreading mutant has bigger impact as shown by purple curve. Even this is nowhere close to second wave.

So the bottom line is: if there is no significantly faster spreading mutant, third wave will be a ripple. And if there is such a mutant, third wave will be comparable to first one.
However, if there is an immunity-escape mutant, all the above scenarios will be invalid!