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Explained: How India’s second Covid-19 wave is different

Coronavirus second wave India: Two metrics illustrate current Covid-19 trends in India. The case fatality rate is lower than during last year’s peak, but this is no relief when the absolute number is so large. And the positivity rate is higher than ever.

Written by Amitabh Sinha
Pune | Updated: April 22, 2021 9:15:05 am
Explained: How second surge is differentMigrant labourers at Thane railway station as Maharashtra announced a lockdown due to Covid-19 spread (Express Photo: Pavan Khengre)

On Friday, close to 1,350 coronavirus-related deaths were reported from across the country, the highest ever. A day later, that number jumped to more than 1,500. The only silver lining in the ongoing second wave — that it was causing fewer deaths compared to last year — is now fast disappearing, with the rapidly-rising infection numbers are leading to more and more deaths.

As a percentage of the caseload, the deaths are still lower than last year, but that is hardly a consolation for a population that is heading towards 2,000 deaths a day in a few days’ time. There are predictions that India’s daily death count could rise to as high as 3,000 a day, which the US used to record during its worst phase. But with no indications yet of any slowdown in the infection rate, the increase in death count is also anyone’s guess.

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In fact, the disease seems to be spreading at faster rate than at any previous time. The positivity rate, which is an indication of disease prevalence in the population, is also at an all-time high, and rising.

No longer the silver lining

The significantly lower mortality rate was the biggest comfort during the second wave which began in the middle of February. Even now, when the daily death count is at record highs, the death rate is much lower than last year. During the previous peak in September, when more than 90,000 cases were being detected every day, India was reporting over 1,200 deaths. Despite the daily count of cases having crossed two lakh, the death numbers were lower than this until two days ago.

Maharashtra, which has the highest counts, offers a good example. The state has been reporting more than 60,000 cases a day, but the death count, over 400 now, is still less than during the peak of last year when it was not reporting even 25,000 cases on any day. The state’s fatality rate this past week is less than half the overall rate. The weekly case fatality rate (CFR) is calculated by comparing the total number of deaths reported in the past one week, with the number of cases detected in the week that ended 14 days previously. The 14-day period accounts for the fact that deaths usually happen two to three weeks after the infection is detected. The weekly CFR presents a current picture of the mortality situation.

Covid-19 in India

The overall CFR, on the other hand, is obtained by comparing the total number of recorded deaths with the total number of confirmed cases as it stood 14 days ago. This offers a more holistic view, and eventually, the deadliness of the epidemic, once it comes to an end, would be judged by its overall CFR.

As of now, Maharashtra has a weekly CFR of 0.89%, while its overall CFR is 2.09%. This kind of situation does not prevail in all states. For example, Delhi, Chhattisgarh, Uttar Pradesh or Gujarat, all of which are in the midst of a big surge, have weekly CFRs that are more than twice their overall CFRs, indicating that the current phase of the epidemic in these states is much more deadly.

For the first time since July, India’s weekly CFR has overtaken the overall CFR. With more than 1.77 lakh deaths, and over 1.4 crore infections, India’s overall CFR stands at 1.42%. This is lower, and therefore better, than in many other countries. In the last one week, more than 7,800 deaths have been recorded, while in the week that ended 14 days ago, about 5.13 lakh cases were detected. That gives a weekly CFR of about 1.53%.

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In the initial weeks of the second wave, a low daily death count was attributed to the circulation of a supposedly milder variant of the virus. However, a more plausible explanation is the fact that over the last one year, there has been a significant improvement in clinical management and critical care infrastructure.

However, the last couple of weeks have seen this infrastructure crumble under the weight of cases. Several deaths have happened because of lack of hospital beds or access to critical care facilities.

Explained: How second surge is different At a Covid-19 ward in Mumbai. (Express photo by Amit Chakravarty)

Faster spread

Over 26.6 crore diagnostic tests have been conducted in India so far. Of these, over 1.47 crore tests, or about 5.5%, have been positive. In the last one week, however, this has increased to over 13.5%.

The seven-day moving average of positivity rate has never been higher.

The current high positivity rate reinforces the possibility that the virus has spread at a much faster rate during the last couple of months, and infected many more people compared to last year. During the first wave, the positivity rate had peaked last July, and then steadily declined even when the positive cases continued to rise in August and September. At that time, the higher number of cases were a direct result of increased tests. Until most of July, India was carrying out less than five lakh tests a day. It was only towards the end of the month that testing numbers began to rise rapidly and climbed to more than ten lakh a day by the third week of August.

Right now, India has been detecting almost 2.5 times as many cases as it was during the September peak. But it is not because of any increase in testing. Testing numbers are roughly at the same level as in September and October last year. But many more people are returning positive.

Maharashtra has had a very high positivity rate, over 15%, for most of the epidemic, but several other states, including Chhattisgarh and Uttar Pradesh, that had relatively lower positivity rates last year — lower than the national average — are now closing the gap. In fact, the weekly positivity rate of Chhattisgarh is currently higher than even Maharashtra’s.

The high rate could be because of increased contact between people or due to the circulation of a faster-transmitting variant. There is evidence that both these things have played a role. A new variant, which has emerged locally and was first noticed in the Vidarbha region of Maharashtra, has two crucial mutations that make it transmit faster and possibly also evade the immune response. More than 60% of the virus samples from Maharashtra collected for gene sequencing show this double mutant strain. This mutant has most likely spread to other states as well.

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