India has been consistently reporting less than 2,000 daily Covid cases for a few days now, much to everyone’s relief. What is the likelihood of a fourth wave of the pandemic? Most studies say that while there could be another wave, the increase in vaccine immunity combined with existing natural immunity places India in a safer position.

The SUTRA model

“Our analysis of a large number of countries has shown that natural immunity provides much better protection against Covid infection than vaccine immunity. Putting these two data together, you can conclude that the chances of any fourth wave are minimal,” says Dr Manindra Agarwal, a professor at IIT Kanpur, who led the group behind the SUTRA model that had predicted the trajectory and peaks of the second and third waves near-accurately.

Their latest report says that atthe beginning of the wave caused by the Omicron variant, 80 per cent of Indians had natural immunity, while only 57 per cent had vaccine immunity. “Right now, well over 90 per cent of Indians have natural immunity against the virus, “ Agarwal says. At the same time, he says, the mathematical model cannot predict a new mutant.

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Reaching an endemic stage?

Talks about a probable fourth wave in India started surfacing after cases steadily rose in countries like China and South Korea. Incidentally, at around the same time, a study by another group of IITK researchers, too, had predicted that a fourth wave will hit India in June. This, however, was dismissed by many experts and the Ministry of Health and Family Welfare. The study is yet to be peer-reviewed.

On Sunday, meanwhile, the World Health Organisation’s Covid-19 technical lead Maria Van Kerkhove said, “The Covid-19 virus is well on its way to becoming endemic, but it doesn’t mean it’s less dangerous or less deadly.” The UN body had recently asked countries to test more and be cautious in lifting Covid curbs.

On the other hand, in a study published in The Lancet, Director of Institute for Health Metrics and Evaluation Christopher JL Murray notes, “After the Omicron wave, Covid-19 will return but the pandemic will not.”

Getting it right

On how the SUTRA [Susceptible, Undetected, Tested (positive), and Removed Approach] model got its predictions nearly right for the second and third waves, Agarwal says, “There were lockdowns that brought down the rate of spread and lifting of lockdowns increased the spread. New mutants, too, changed the parameters.” He adds that a lot of earlier models used parameters that hold good only for a homogenous population. He said the ICMR’s sero surveys too helped the team arrive at estimates quite accurately.

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