Since my first post last on the exponential growth in the spread of the Coronavirus several days ago, it has continued its exponential growth. The US continues to experience average daily growth at about 33% and is growing faster than any other country. The graph below shows cumulative growth for six countries since March 1st. All countries are normalized to start at 1 on March 1st, which means that cases in the U.S. have grown by a multiple of over 300 in the first three weeks of this month.
Exponential growth is illustrated in a fable about chess. According to lore, this game was invented in India around 1,500 years ago. The king greatly enjoyed the game and wished to reward the inventor. When summoned before the king the inventor asked for an increasing amount of rice. On the first day, he wanted one grain of rice and then for this amount to double every day for 64 days, equal to the number of squares on a chessboard. The king thought it a paltry prize but agreed. After 21 days the number of grains was 1 million. That’s the amount of grains in 47 1-pound bags of rice, not a huge sum. However, 14 days later, the number of grains was over 17 billion. That is 780,000 bags of rice, which is 16,000 times the number on day 21.
Even at our fast rate, the number of total reported cases is not doubling every day. The number in the U.S. in doubling every 2.4 days. Two weeks from now at the current rate, the number of cases will have increased by 56 times, from 24,207 on March 21 to more than one million in two weeks. There is a lot of uncertainty around that. It could be more or less. Given the lag in testing, the number of people infected in the U.S. may already be that high. People are taking some steps to slow the spread. But we are not on a complete lock down, unlike Italy, France, and Spain – whose rates are all slowing. Hopefully our rate of growth will start to slow soon, but we need to do more.
This post was inspired by your comments. Thanks to everyone who has commented – keep them coming!