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As cases drop, experts say spread may be more than what is known

For over a month-and-a-half now, reported cases of the infection have dropped to below 50,000 a day. During this time, there have been festivals, elections, farmers’ protests, and relaxations in restrictions.

Written by Amitabh Sinha | Pune | Updated: December 14, 2020 8:02:02 am
As cases drop, experts say spread may be more than what is knownAt a screening centre in Hyderabad on Sunday. (PTI)

With new infections of Covid-19 having seemingly stablised for over a month now, experts believe that a larger share of Indian population may have already been infected by the virus than what serosurveys have been indicating.

For over a month and a half now, reported cases of the infection have dropped to below 50,000 a day. During this time, there have been festivals, elections, farmers’ protests, and relaxations in restrictions.

All this was feared to result in a surge in the number of people being found to be infected. But not only has there been no surge, the numbers have been on the decline, slowly but steadily. For the last two weeks, the daily detection of new cases has remained firmly below 40,000. Follow Coronavirus India Live Updates

The largest number of cases are still coming from Kerala and Maharashtra, each reporting about 4,000 to 5,000 cases a day, while a state like Bihar, where the numbers were expected to rise due to elections and Chhath, has been reporting barely 500 to 600 cases a day.

Experts say that the only logical way to explain this could be that a much higher proportion of the population than we currently know of, may be even more than half the entire population of the country, might already have been infected.

“In fact, the predictions of a computer model that we have developed actually tells us this. As of Saturday, this model has been suggesting that close to 55 per cent of Indian population might have been infected,” said Manindra Agarwal of IIT Kanpur. “Now, none of the serosurveys are capturing such large numbers for disease prevalence. And we don’t know what could be the reason”

Agarwal was part of a government-appointed committee that had developed a ‘supermodel’ to map the trajectory of the disease in India. In mid-October, this committee had released the findings of its modelling exercise, and had said the epidemic had already ‘peaked’ in India, and was likely to run its course by February next year.

Shahid Jameel, a virologist and director of Trivedi School of Biosciences at the Ashoka University, agrees that it is possible that the actual prevalence of disease is much higher than what the sero-surveys have been able to capture.

“The last national sero-survey showed that the actual disease prevalence could be 15 to 16 times higher than the confirmed cases. With 10 million confirmed cases now, it would mean that about 150 to 160 million might have actually been infected. But it is possible that the outbreak has moved faster than we have been able to record. Because of that it could be that instead of 150 to 160 million people, 400 or 500 million have been infected. I think it is a good time to call for another broad sero-survey,” Jameel said.

“Another possibility for which again we do not have any evidence is that the virus might have lost some of its virulence because of this increasing number of exposures. This does happen with viruses, but is usually vaccine-driven,” he said.

Agarwal also offers a possible explanation for the low numbers in Bihar, and the recent third wave in Delhi.

“Our model shows that the disease prevalence in Bihar has reached as high as 65 per cent. In fact, for every confirmed case of infection, there might be 300 that are unreported. This ratio is the highest in Bihar. Now, if that is true, it would be able to explain why Bihar is reporting only about 500 cases a day,” he said.

In Delhi, Agarwal said, the model showed that for every confirmed case, about 40 cases went unreported. “Around the time that Delhi had been reporting very high numbers a few weeks ago, we found that this ratio had changed to about one in 20. And what we discovered during this time is that Delhi had changed its testing strategy. It had made testing free of cost, and removed restrictions on who could be tested. As a result, a lot of people who felt even mild symptoms went ahead and got themselves tested. And that led to a rise in the number of reported cases. The third wave in Delhi was not a real increase in the spread of the disease, but more likely just a consequence of a change in testing policy,” he said.

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