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.