The Homa Files

Practically every time Dr. Fauci — the CDC’s undisputed truth teller — speaks, he references “flattening the curve”.

Graphically, here’s what he talking about…

Source: The Lancet

Let’s drill down on the chart…

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The chart is simply an application of classical “diffusion theory” — oft used to explain the adoption of new innovations and the spread of communicable diseases.

Focusing on the red “base case” line above, the curve is mathematically driven by 3 main factors: (1) the number of “starter” cases (2) the replication rate, and (3) the length of the replication cycle.

Let’s take a simple example … assume that we start with one case, that each case replicates (i.e. “infects”)  2 additional cases and that it takes 1 day for the virus to replicate.

Given those parameters, we’d start with 1 case … have 3 cases in the 2nd day (the original case plus the 2 replications) … 7 cases in the 3rd day(the original case plus its 2 replications plus 4 replications off the 1st days replication) … and so on.

The big takeaway is displayed below: the cumulative number of cases grows very rapidly … in mathspeak: “exponentially” based on the replication rate.

Eventually you run out of people susceptible to infection and the curve peaks. Again, see the red line above.

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So, how to “flatten the curve”?

Answer: Focus on the curve-driving factors:

1. Impede the number of starter cases, e.g. by banning travelers from existing hot spots.

2. Reduce the replication rate, e.g. by strictly quarantining known contagious patients … and by “social distancing” — keeping uninfected people out-of-reach of non-quarantined contagious people.

By doing the above, the contagion isn’t eliminated … but its diffusion curve is flattened: the peak is lowered and delayed, i.e. time-shifted until later … and the whole curve is spread over a longer time period (i.e. its effect gets “diffused”). See the green line above.

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Even though the total contagion isn’t reduced, fattening the curve has 3 major benefits:

1. It reduces the immediate demand on healthcare facilities … spreading it out over a longer time frame.

2. It buys time to produce short-supply medical equipment, meds and supplies

3.  Maybe, it even buys enough time for virus-treating therapies to be developed and launched.

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For an excellent scientific recap, see:

How will country-based mitigation measures influence the course of the COVID-19 epidemic?

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This entry was posted on March 15, 2020 at 9:20 am and is filed under Coronavirus - Covid 19. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.