Tamil Nadu

A question of susceptibility: why cases did not soar after Deepavali

The Tamil Nadu Pollution Control Board reported a substantial drop in the values of major pollutants in Chennai on November 14, 2020.   | Photo Credit: R. Ravindran

Why did the anticipated rise in COVID-19 cases post the over-crowding witnessed during Deepavali not happen? Epidemiologists and virologists advance a few theories that together may explain the drop in the number since then.

In the 18 days between November 14 (Deepavali day) and December 1, there were 28,859 new cases in Tamil Nadu. In contrast, in the 18 days between October 27 and November 13, there were 42,747 cases. This fall has overjoyed, and yet foxed, health managers.

Jacob John, former professor and HOD, Clinical Virology Department, CMC Hospital, Vellore, says what has shifted is essentially the equation between the susceptible (likely or liable to be infected) people and the non-susceptible people, with the latter increasing. Owing to this, the speed with which the virus can travel has markedly reduced, he adds. He further explains: If one person infected earlier could transmit the infection to four people, and now, if three of them are not susceptible to the infection, only one out of the four will be infected. It is possible then that the trend would be downwards, slowing down post festival, he adds.

Second wave possible?

Is a second wave a possibility in Tamil Nadu? He says: The second wave is a reality in Italy, Germany, South Korea, New Zealand, or Kerala, wherever the first wave was successfully flattened, and the infection was not allowed to reach a natural peak. So more people remained susceptible in the community.

In the course of the epidemic, in June, there was a mutation that made the virus more transmissible. The proportion of the susceptible people versus the non-susceptible people was higher in these places because the infection was suppressed in the first wave. The second wave was stronger, therefore, in these places.

“In India, however, we let the virus [have a] free passage... So it possibly wasn’t flattened during the first phase. My hunch is that we may not have a second wave, but we’ll need to wait and watch how this phase proceeds.”

The fall in the number of deaths, also witnessed in Tamil Nadu, seems to be part of a universal phenomenon, Dr. John says. Three scenarios are possible. First, those who are at risk have already died of the infection and the remaining are less prone to the infection, and secondly, doctors have learnt to manage the disease better. They have learnt to look at oxygen levels early, look for blood clots, anticipate the signs and treat early. Healthcare has certainly improved from the early months of the pandemic. “The third possibility is that there is a reduction in viral virulence. This is a theoretical possibility though, and is difficult to study. The national emergence of a new agent in a new host may lead to a higher transmission and low deaths. We don’t know much about localised immunity,” he says.

Health Minister C. Vijayabaskar says slowly lifting the restrictions during the lockdown and using the tapering-off method have had a positive impact. “We have our surveillance study ongoing and once we have the results of the study, we’ll be able to tell what percentage of the population already has had the infection,” he adds. He agrees that further studies are required to test whether there is a milder form of the virus at work.

Health Secretary J. Radhakrishnan says there should be no let-up in vigilance. While messages are constantly being communicated to district health authorities and the Collectors to keep the number of tests up, following the protocol — masking, physical distance and hand hygiene — too should be emphasised.

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Printable version | Jan 27, 2021 12:33:18 PM | https://www.thehindu.com/news/national/tamil-nadu/a-question-of-susceptibility-why-cases-did-not-soar-after-deepavali/article33235483.ece

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