What does it mean to “flatten the curve”, in the context of an epidemic? Here is Willis Eschenbach’s interpretation:

What does “flattening the curve” mean? It is based on the hope that our interventions will slow the progress of the disease. By doing so, we won’t get as many deaths on any given day. And this means less strain on a city or a country’s medical system.

Be clear, however, that this is just a delaying tactic. Flattening the curve does not reduce the total number of cases or deaths. It just spreads out the same amount over a longer time period. Valuable indeed, critical at times, but keep in mind that these delaying interventions do not reduce the reach of the infection. Unless your health system is so overloaded that people are needlessly dying, the final numbers stay the same.

I beg to differ. Or, at least, to offer a different interpretation: Flattening the curve — reducing its peak — can also reduce the total number of persons who are potentially exposed to the disease, thereby reducing the total number of persons who contract it. How does that work? It requires not only reducing the peak of the curve — the maximum number of active cases — but also reducing the length of the curve — the span of time in which a population is potentially exposed to the contagion.

Consider someone who has randomly contracted a virus from a non-human source. If that person is a hermit, the virus may kill him, or he may recover from whatever illness it causes him, but he can’t infect anyone else. Low peak, short duration.

Here’s an example of a higher peak but a relatively short duration: A person who randomly contracts a virus from a non-human source then infects many other persons in quick succession by breathing near them, sneezing on them, touching them, etc., in a short span of time (e.g., meeting and greeting at a business function). But … if the originator of the contagion and those whom he initially infects are identified and quarantined quickly enough, the contagion will spread no further.

In both cases, the “curve” will peak at some number lower than the number that would have been reached without isolation or quarantine. Moreover, and more important, the curve will terminate (go to zero) more quickly than it would have without isolation or quarantine.

The real world is more complicated than either of my examples because almost all humans aren’t hermits, and infections usually aren’t detected until after an infected person has had many encounters with uninfected persons. But the principle remains the same: The total number of persons who contract a contagious disease can be reduced through isolation and quarantine — and the sooner isolation and quarantine take effect, the lower the total number of infected persons.