There’s an old brain teaser that goes like this: You have a pond of a certain size, and upon that pond, a single lilypad. This particular species of lily pad reproduces once a day, so that on day two, you have two lily pads. On day three, you have four, and so on.
Now the teaser. “If it takes the lily pads 48 days to cover the pond completely, how long will it take for the pond to be covered halfway?”
The answer is 47 days. Moreover, at day 40, you’ll barely know the lily pads are there.
In this article by journalist Megan McArdle, published in the Washington Post, she says that this grim math explains why so many people — including herself — are worried about the novel coronavirus, which causes a disease known as covid-19. And why so many other people think we are panicking over nothing.
During the current flu season, they point out, more than 250,000 people have been hospitalized in the United States, and 14,000 have died, including more than 100 children. As of this writing, the coronavirus has killed 29 people, and our caseload is in the hundreds. Why are we freaking out about the tiny threat while ignoring the big one?
Go back to those lily pads, McArdle writes: When something dangerous is growing exponentially, everything looks fine until it doesn’t. In the early days of the Wuhan epidemic, when no one was taking precautions, the number of cases appears to have doubled every four to five days.
The crisis in northern Italy is what happens when a fast doubling rate meets a “threshold effect,” where the character of an event can massively change once its size hits a certain threshold.
In this case, the threshold is things such as ICU beds. If the epidemic is small enough, doctors can provide respiratory support to the significant fraction of patients who develop complications, and relatively few will die. But once the number of critical patients exceeds the number of ventilators and ICU beds and other critical-care facilities, mortality rates spike.
So everyone needs to understand a few things, according to McArdle.
First, the virus is here, and it is spreading quickly, even though everything looks normal. Right now, the United States has more reported cases than Italy had in late February. What matters isn’t what you can see but what you can’t: the patients who will need ICU care in two to six weeks.
Second, this is not “a bad flu.” It kills more of its hosts, and it will spread farther unless we take aggressive steps to slow it down, because no one is yet immune to this disease.
Third, we can fight it. Despite early exposure, Singapore and Hong Kong have kept their caseloads low, not by completely shutting down large swaths of their economies as China did but through aggressive personal hygiene and “social distancing.”
Fourth, and most important: We are all in this together.