April 7, 2021The PrinthealthCovid-19

Why my estimates for the second wave of Covid-19 were wrong

While I had qualified my assessment with a few caveats, I was wrong to expect that the second wave will be “small” in several cities and districts. I did not anticipate that people would so quickly relax their guard, engage in large gatherings and visit crowded places.

The Print This is from my weekly column in The Print (2018-2021)

Important Note:

My estimates turned out to be very wrong. India suffered a massive second wave that caused great pain and anguish, and claimed the lives of many of our friends and loved ones. The risk with any model is that we are working with terribly sparse and unreliable official data. This makes any estimate hazardous. Yet, public policy and the general public need some sense of what to expect — and an answer that it is unpredictable” does not help.

My simple method successfully predicted when the first wave would taper out. With that confidence I tried to forecast the second wave. Unfortunately, I got it wrong. Why? In July 2021 I know what I didn’t in January: that the December 2020 holiday attracted massive crowds (Goa was swarmed), a new and deadlier Delta variant had probably emerged, the Kumbh Mela and political rallies spread it further and vaccination procurement was small.

I have always argued against analysts trying to predict the future, contending that it is better to prepare for all eventualities and manage the consequences instead. In writing these pieces, I violated my own injunctions.

In this piece written in late-March 2021, I admit my mistake and try to explain why I might have gotten it wrong. We have more information now than I had at the time of writing.

The primary reason for a resurgence in coronavirus cases, beginning March 2021, is that people who had previously protected themselves well relaxed their guard by increasing their movements, attending classes or workplaces and engaging in social and religious gatherings. The fraction of the population that had isolated itself in 2020 is increasingly becoming exposed to the coronavirus in 2021. As can be seen from the data, the second wave” is occurring in places where mask wearing, hand hygiene and social distancing was relatively better in 2020. While newer strains of the virus that are more contagious have contributed to the surge, it is the change in human behaviour that is the more important cause.

For instance, in a city where say 20 per cent of the population took adequate protective measures in 2020, the first wave would have come to an end after say, 70 per cent of the poorly protected 80 per cent (that is 56 per cent of the overall population) developed antibodies. Thus, cases would have reduced to a trickle by January 2021, but with 44 per cent of the city’s population still susceptible to the virus. If and when these people relaxed their guard, the second wave began.

Note that there are second waves in certain localities around the country’; it is not very accurate to talk of a second wave in India’.

When will the second wave subside?

The second wave will subside when a large proportion of the exposed population develops immunity, either through infection or through vaccination. These include both who protected themselves well in 2020 and those who did not but were fortunate to escape infection.

In the above example, the second wave will subside when around 70 per cent of the 44 per cent residual population of the first wave (that is, 31 per cent of the overall population of the city) acquires antibodies.

How long this will take depends on how big the first wave was and how fast the new infection rate is. By my cynically optimistic back of the envelope (COBOTE) estimates, for cities like Mumbai and Bengaluru, (assuming 10 per cent of the population protected itself properly last year; real cases were 20 times larger than official cases; and an average second wave doubling rate of 20 days) this wave should exhaust itself in around 40 days from now, perhaps faster. This assumes the current pace and strategy of vaccination.

How can the second wave be contained? If 50 per cent of the susceptible population in these cities is vaccinated, the second wave can be contained much faster — within a week in Mumbai, and around three weeks in Bengaluru. This will also prevent subsequent waves in the future. There is thus a case for sharply targeted universal vaccination programmes in affected cities like Mumbai, Pune, Bengaluru, Delhi.

Were you not wrong when you argued that India will not have a major second wave?

In January 2021, I had argued that it is unlikely that we will have a significant second wave’ across the country, although there will be small second waves in several cities and districts. This does not mean we can drop our guard and get back to pre-pandemic levels of congregation; rather, it means that if we continue to be careful, we will all be safe a few months down the road.”

While I had qualified my assessment with a few caveats, I was wrong to expect that the second wave will be small” in several cities and districts. I did not anticipate that people would so quickly relax their guard, engage in large gatherings and visit crowded places. The COBOTE model was good enough to estimate when the first wave would end, so I’ve used it again to make estimates for the second wave. Note that this is merely an extremely rough measure to get a better sense of the spread. I am sharing these assessments because some clarity is better than complete uncertainty.

Is a faster second wave better?

While a faster second wave might appear desirable for things will calm down sooner, the problem is that it will exhaust healthcare capacity quickly. This is already happening in many affected cities. Flattening the curve” by masking, social distancing and containment strategies is necessary to ensure healthcare facilities are available. This means a longer wave, as we saw last year, but a less lethal one. So well-considered and targeted containment strategies are necessary.

The rest of my The Print columns are here

Why has there been a second wave of coronavirus? The best option, of course, is rapid universal adult vaccination in all second-wave-hit cities and districts. This will both shorten the second wave and reduce the burden on hospitals and medical facilities. We must pursue the vaccination campaign on a war footing.

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