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‘Third wave of Covid-19 will not be big if immune-escape mutant does not emerge’

TV Jayan New Delhi | Updated on July 07, 2021

IIT Kanpur prof designs simulation model to assess virus behaviour

If a fully immune-escape variant of SARS-CoV2 doesn’t surface, the third Covid-19 wave will only be a ripple when compared to the second wave that killed more than 2.5 lakh in a short span of time, according to a mathematician who has been instrumental in designing a simulation model to assess the virus behaviour.

“Presuming that the vaccination roll out happens as expected and the new mutant that comes is only 25 per cent more infectious but not immune-escape one, the third wave will only be a ripple, which, at best, is comparable to the first one,” said Manindra Agrawal, professor of computer science at the Indian Institute of Technology (IIT) Kanpur.

Sutra model

Agrawal, together with Mathukumalli Vidyasagar of IIT-Hyderabad, and Madhuri Kanitkar, Deputy Chief of Integrated Defence Staff, designed Sutra, the model that guided the government in taking several pandemic responses in the past.

Agrawal said even if there is no lockdown, the effect doesn’t look to be very severe. The scientists worked out three different scenarios with their model.

This is despite the scientists assuming that 50 per cent of the fully vaccinated people are still susceptible and 20 per cent of those infected by Delta variant (primarily responsible for the second wave) vulnerable again. However, this situation can change significantly if there is a variant that is fully immune escape.

‘Back to square one’

“Then we are back to square one. Like in March last year in which everybody is susceptible,” Agrawal told BusinessLine. “The key thing here is the assumption that 20 per cent of those infected by the Delta variant in the second wave becomes susceptible again after three months. If that numbers increases dramatically, to say, 90 per cent, then we may have to call it a new pandemic,” he said.

First sero survey

Agrawal was candid to admit that the Sutra model failed to pick up the extent of the second wave. This was because the scientists had used the results of the first sero survey, spearheaded by the Indian Council of Medical Research, for calibrating their model.

“With that calibration our model was showing well above 50 per cent of the population was immune. This made us calculate the second wave would not be very big and, at best, it would be similar to the first one,” he said. This turned out be way off the mark, he said.

After realising that the calibration was wrong, the scientists subsequently calibrated the model with the latest ICMR survey of December 2020-January 2021. “With this calibration, our study shows nearly 60 per cent of the Indian population is now immune, which is corroborated by other studies includind one by the All India Institute of Medical Sciences, New Delhi,” said Agrawal.

“Our model has a very nice property that nearly all parameters, except one calibration point computes on data. Already in Febraury we knew there is a variant running around in Maharashtra, which is more infectious; in fact, much before any virologist had flagged it. Our data was saying it, but we were not sure because nobody else was saying it,” he said.

Published on July 06, 2021

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