If life continued without change, on average, someone with COVID-19 might infect somewhere around 3 others. And it takes about 6 days, say a week, for someone to infect others.

So in two months just from that one person we go from 1 to 3 to 9 to 27 to 81 to 243 to 729 to 2187. All from one person.

With social distancing suppose that we reduce this to 2. Now in 2 months we go from 1 to 2 to 4 to 8 to 16 to 32 to 64 to 128. Still explosive growth but 128 is about twenty times less than 2187. While most people who are infected don’t need to be hospitalized, there are still twenty times as many hospitalizations if we do nothing.

In fact we want to reduce this number (called R0 or R-naught) to way less than 2. If it is 1.25, then after 8 weeks we expect about 5 cases. And if we keep it less than 1, the epidemic will die out.

That’s why governments are introducing drastic measures. If we keep the growth down, the hospitals can better handle the cases. We can better learn how to treat cases. We can do studies to find what treatments really work and which give false hope. And it buys us time to evaluate vaccines.