Exponential growth makes India the global COVID hot spot | Science | In-depth reporting on science and technology | DW | 29.04.2021

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Exponential growth makes India the global COVID hot spot

India has seen over 300,000 new COVID-19 infections every day for a week. Exponential growth could become a problem — not just for India: but for the world, as well.

Indian women in traditional saris sitting on the chequered floor of the Peacock courtyard at the City Palace Complex in Udaipur.

The chessboard formula is causing concern not only for epidemiologists in India, but worldwide

The number of newly infected people in India is shocking: On Thursday, the country reported more than 386,000 new infections daily ― the highest total worldwide.

The situation has been exacerbated by the new "double mutant," B.1.617, which combines two mutations in the spike protein. Since the beginning of April, the number of infections has exploded.

In the medium term, this exponential growth could become a problem not only for India and its neighboring countries, but for the rest of the world, as well.

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What does exponential growth mean in relation to the coronavirus?

To illustrate exponential growth, there is a very appropriate legend from India of timeless validity: A long time ago, the ruler Shihram tyrannized his subjects and great misery reigned.

In order to make Shihram aware of the grievances, the wise brahmin Sissa invented the game of chess, with its 64 squares, in which the king is the most important character, but without the support of the pawns and the other pieces, he can do nothing. The king liked the game and wanted to reward the inventor. The clever Sissa wished that on the first square of a chessboard a grain of wheat be placed, on the second square double, i.e., two, on the third again double, or four, and so on.

The emperor felt offended in view of the brahmin's supposed modesty, since he was not yet aware of the extent of the wish. It took days for the court arithmeticians to calculate the required amount of wheat grains. In the end, the overseer of the granary informed the king that so much wheat could not be raised in the whole realm.

The clever brahmin would have had to get what would amount to about 730 billion tons of wheat, roughly a thousand times the world wheat harvest of last year.

What does the chessboard formula mean for the pandemic?

If we apply the chessboard formula to the pandemic, this would correspond to a contagion rate (reproduction number R) of 2: Each infected person would infect two other people. 

Exponential growth explained in an infographic

India is home to about 1.34 billion people. Nearly 19 million are currently infected with the coronavirus. Fortunately, the reproduction number R for COVID-19 is usually much lower than in the chessboard formula. In India, it is currently 1.32, according to a report by the daily India Today.

The value is highly dependent on people's behavior and social factors: whether they maintain distance and strict hygiene, whether they live in crowded conditions, and under what circumstances they work. In India, for example, the value R was much higher (1.83) during the first wave in March 2020 than it is now.

Still, at the current rate, the number of infected people is expected to double quickly.

More infected, more dead

As the number of infections rises exponentially, the number of deaths is also increasing rapidly. To date, more than 200,000 people in India have died of COVID-19. The mortality rate is 1.14%. So if 1.14% of the 18 million people currently infected die, that would be another 205,200 deaths. If the number of infected people doubles, that's an additional 410,400 deaths.

And, as the coronavirus doesn't stop at national borders, the B.1.617 variant and the exponential growth of new infections on the Indian subcontinent are rightly causing concern not only there — but worldwide.