Michael Levitt, an American-British-Israeli biophysicist who won the 2013 Nobel prize for chemistry for "the development of multiscale models for complex chemical systems," has become something of a household name in China over the last few months. Although his specialty is not in epidemiology, he accurately forecast the slowing down of the spread of the virus in February, giving hope to those affected by the lockdown.
But far from being a modern-day prophet, he explained in an interview with Calcalist that he simply crunched the numbers.
Levitt's wife, Shoshan Brosh, is a researcher of Chinese art, meaning that the couple regularly travels between America, Israel and China. Consequently, when the virus broke out in Hubei province, Levitt wrote to his Chinese friends in support.
“When they answered us, describing how complicated their situation was, I decided to take a deeper look at the numbers in the hope of reaching some conclusion,” Levitt explained. “The rate of infection of the virus in the Hubei province increased by 30% each day — that is a scary statistic. I am not an influenza expert but I can analyze numbers and that is exponential growth.”
Had the growth continued at that rate, the whole world would have become infected within 90 days. But as Levitt continued to process the numbers, the pattern changed. On February 1, when he first looked at the statistics, Hubei Province had 1,800 new cases a day. By February 6, that number had reached 4,700 new cases a day.
But on February 7, something changed. “The number of new infections started to drop linearly and did not stop," Levitt said. "A week later, the same happened with the number of the deaths. This dramatic change in the curve marked the median point and enabled better prediction of when the pandemic will end. Based on that, I concluded that the situation in all of China will improve within two weeks. And, indeed, now there are very few new infection cases.”
Levitt likened the trend to diminishing interest rates: if a person receives a 30% interest rate on their savings on Day 1, a 29% rate on Day 2, and so on, “you understand that eventually, you will not earn very much.”
Similarly, although new cases are being reported in China, they represent a fraction of those reported in the early stages. “Even if the interest rate keeps dropping, you still make money," he said. "The sum you invested does not lessen, it just grows more slowly. When discussing diseases, it frightens people a lot because they keep hearing about new cases every day. But the fact that the infection rate is slowing down means the end of the pandemic is near.”
By plotting the data forward, Levitt has predicted that the virus will likely disappear from China by the end of March.
THE REASON for the slowdown is due to the fact that exponential models assume that people with the virus will continue to infect others at a steady rate. In the early phase of COVID-19, that rate was 2.2 people a day on average.
“In exponential growth models, you assume that new people can be infected every day, because you keep meeting new people," Levitt said. "But, if you consider your own social circle, you basically meet the same people every day. You can meet new people on public transportation, for example; but even on the bus, after some time most passengers will either be infected or immune.”
However, that doesn't mean Levitt is dismissive of the precautions being put in place by governments around the world.
“You don’t hug every person you meet on the street now, and you’ll avoid meeting face to face with someone that has a cold, like we did,” Levitt said. “The more you adhere, the more you can keep infection in check. So, under these circumstances, a carrier will only infect 1.5 people every three days and the rate will keep going down.”
Isolation and limiting social contact is not the only factor at play, however. In Wuhan, where the virus first emerged, the whole population theoretically was at risk of becoming infected, but only 3% were.
The Diamond Princess cruise ship represented the worst-case scenario in terms of disease spread, as the close confines of the ship offered optimal conditions for the virus to be passed among those aboard. The population density aboard the ship was the equivalent of trying to cram the whole Israeli population into an area 30 kilometers square. In addition, the ship had a central air conditioning and heating system, and communal dining rooms.
“Those are extremely comfortable conditions for the virus and still, only 20% were infected. It is a lot, but pretty similar to the infection rate of the common flu,” Levitt said. Based on those figures, his conclusion was that most people are simply naturally immune.
Looking at the picture globally, Levitt was reticent to make predictions country-by-country as to when the spread of the virus will slow. China is nearing the point at which the number of new infections will be zero, while South Korea had already moved past the median point, and was starting to see a slow down in new infection rates.
Italy's higher death rate, he said, was likely due to the fact that elderly people make up a greater percentage of the population than they do in other countries such as China or France. “Furthermore, Italian culture is very warm, and Italians have a very rich social life. For these reasons, it is important to keep people apart and prevent sick people from coming into contact with healthy people.”
Israel doesn't have enough cases to provide useful data from which to make predictions, Levitt said, although he praised the government for its preventative measures. "The more severe the defensive measures taken, the more they will buy time to prepare for needed treatment and develop a vaccine,” he said.