"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.”