Post #958: About a third of U.S. residents have already had COVID

Posted on January 17, 2021

In the spirit of “it can’t get but so much worse”, here’s an estimate of the fraction of the U.S. population that has already been infected with COVID-19.

As of today (1/17/2021), about 24 million cases have been reported.  It is well- established that there are several actual infections for every one that is reported.  That’s due to asymptomatic and mildly symptomatic individuals who don’t bother to go to a doctor about their symptoms, and so don’t get tested.

Here, I am assuming a conservative five-to-one ratio between total infections and formally-diagnosed infections.  That five-to-one splits the difference between two different estimates from CDC staff, as documented in Post #940.  A CDC estimate based on likelihood of getting tested would put that ratio at closer to 8-to-1.  A CDC estimate based on presence of antibodies in a recent (non-random) sample of blood draws would put it closer to 4-to-1.  I chose 5-to-1 as a seemingly reasonable estimate, as documented in that post.