Third Covid wave in India to be a ‘ripple’ if there’s no fast-spreading mutant: Study

July 2, 2021 John Ripple 0

The third wave of Covid-19 in the country will be a “ripple” if there is no significantly faster-spreading mutant, projections of the ‘Sutra’ model say. According to the Sutra analysis, if there is such a faster-spreading mutant, the third wave will be “comparable to the first one”.

The scientists behind the ‘Sutra Model’ were earlier part of an expert panel set up by the Department of Science and Technology under the Government of India.

Three members of this erstwhile government panel came up with the ‘Sutra Model’ last year and has since made mathematical projections on the trajectory of the Covid cases. This is the ‘Susceptible, Undetected, Tested (positive), and Removed Approach’ (Sutra) to study the trajectory of the pandemic.

Maninder Agarwal, professor, IIT Kanpur, who was part of the team of scientists behind thia Sutra analysis, said that they have created three scenarios:

1. The optimistic one: Where we assume that life goes back to normal by August, and there is no new mutant.

2. The intermediate one: Where we assume that vaccination is 20 per cent less effective in addition to optimistic scenario assumptions.

3. The pessimistic one: This has one assumption different from intermediate one: a new, 25 per cent more infectious mutant spreads in August (it is not Delta Plus, which is not more infectious than delta).

“if there is an immunity-escape mutant, all the above scenarios will be invalid,” the Sutra model says.

The IIT professor explained using a chart, the plots for the three scenarios. Blue curve is actual data, orange one is model prediction until May, and dotted curves are three scenarios plotted from June.

Professor Maninder Agarwal said there is hardly any difference between optimistic and intermediate scenarios, suggesting vaccine efficacy changes do not have a significant impact. “A faster-spreading mutant has bigger impact as shown by purple curve. Even this is nowhere close to second wave,” the professor said.

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“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!,” he added.

The analysis

The IIT Kanpur professor said it took them 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,” he said.

It turned out that both can be incorporated by suitably changing contact rate and reach parameters. So that takes care of third one, he said, adding that the first two required detailed analysis.

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“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,” he added.

“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,” he said.