How Many Americans Currently Have the Virus?

  • Per IHME, the covid modeling outfit at the U. of Washington: Daily deaths is the best indicator of the progression of the pandemic, although there is generally a 17-21 day lag between infection and deaths… For estimated infections, we start with death estimates, then work backward, using infection fatality ratios to estimate infections based on deaths.
  • IHME uses an infection fatality ratio of around 0.85%. So, for every person who dies of covid, there have been around 1/.0085 = 118 people who’ve been infected.
  • Per CDC and WHO, people who’ve been infected remain contagious for around 10 days on average.
  • Over the 10-day interval from August 20-30, 9,234 Americans died of covid. 9,234 deaths x 118 infections per death = 1.1 million people in the US were infected and contagious during the 10-day interval from around August 3-13. The death rate has been pretty steady for most of August, so assume 1.1 million Americans are currently infected and contagious.
  • Population of the US = 328 million. 1.1M/328M = 0.34% currently infected and contagious in the US.
That doesn’t seem like a high prevalence. But assuming a steady state of epidemic contagion, within ten days the 1.1 million people currently infected will pass the virus on to another 1.1 million before recovering (or dying), and so on. As of the end of August, 6.7 percent of Americans have been infected since the beginning of the epidemic. By the end of September it’ll be 7.7 percent; by the end of November, 8.7 percent…

 

3 thoughts on “How Many Americans Currently Have the Virus?

  1. In estimating US cumulative infections as of the end of August, I used death rate as the lagging indicator but failed to compensate for the lag. I.e., the death total on August 31 represents 0.85 percent of Americans who had been infected maybe 3 weeks before that. So to the 8/31 death total I should add 3 weeks’ more deaths, projecting from the current weekly rate, then multiply by 0.85% to get the 8/31 estimated infection rate. That recalc increases the 8/31 cumulative US infection estimate to 7.3 percent.

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  2. According to the CDC’s Pandemic Planning Scenarios, the time from infection to symptom onset is about 6 days, and the time from symptom onset to death is about 14 days — so there’s the 20-day lag. However, there’s another lag I’d not factored in: the average time from death to reporting of the death, which is another 20 days. So, to use death as a lagging indicator of cumulative infection, it’s necessary to add 40 days’ worth of projected deaths to the current cumulative death total. That would increase the end-of-August cumulative infection estimate for the US to about 7.9 percent.

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