Almost a month ago, in my post on expert analysis, I highlighted a model by Richard Neher that looked at the possible global spread of SARS-CoV-2 infections based on numerous seeding events. At that time, many observers were reporting the good news that the rate of increase in the number of infections in Hubei province was declining.
That declining rate of increase was expected given the extreme quarantine measures taken in Wuhan and other cities. However, it was also clear that smaller outbreaks were being seeded elsewhere.
Neher ran simulations to get a handle on this scenario, using his educated guesses for the relevant parameters. He assumed then that many such outbreaks were already underway, and that they were running 2 or 3 months behind the Wuhan outbreak. With increased awareness among the public and health-care workers, he assumed that many of the new outbreaks would grow more slowly than Wuhan’s did and be contained. (As seems to have happened in Singapore.) And even those that grow large would, like Wuhan, slow down once they had become very large due to quarantines and other social distancing. (As seems to be be happening in South Korea.) Nevertheless, Neher found it was possible to envision total global cases in several months that would dwarf those seen in Hubei, even while it looked then as though the rate of increase was declining. I’ve re-posted a screen shot of Neher’s scenario below.
Here, for comparison, is a screenshot of a new graphic produced by CNBC using data from Johns Hopkins University. It’s still too early to say how the numbers will play out over time. Even right now, the total number of infections globally is very uncertain, with many countries (including the USA) lagging in testing for the virus. But qualitatively, at least, Neher’s model prediction is–unfortunately–looking all too real.
ADDED: As Richard Neher adds: “I want to point out that the simulations we did 4 weeks ago assumed limited infection control measures and essentially model unchecked growth. China has shown that drastic measures can change the course of a COVID-19 epidemic.”