Enter August: The Virus is On a Roll

Remember when people were worried about a second wave of the virus hitting the US in the fall?

Here’s the estimated Rt, the coronavirus’s effective reproduction rate, based on changes in daily death rates over consecutive ten-day intervals:

  • July 22 — August 1:   1,118/843 = 1.33
  • July 12 — July 22:   843/633 = 1.33
  • July 2 — July 12:   633/630 = 1.00
  • June 22 —  July 2:    630/599 = 1.05
  • June 12 —  June 22:   599/853 = 0.70
  • June 2 –  June 12:   853/940 = 0.91
  • May 23 –  June 2:   940/1,316 = 0.71
  • May 13 –  May 23:   1,316/1,700 = 0.77

More than 158 thousand Americans have died from coronavirus. Based on a mortality rate of 0.6 percent, about 8 percent of the US population has been infected since the beginning of the epidemic, with 1.8 million being currently infected and contagious.

At the present Rt, those 1.8 million people will over the next ten days transmit the virus to 2.4 million more people; those 2.4 million will in turn infect another 3.2 million, and so on, increasing geometrically. By the end of the year three-quarters of the US population will have been infected — i.e., herd immunity — with 2.6 million Americans having died of the virus. To put that death toll in perspective, last year 2.9 million Americans died from all causes combined.

An alternative estimate of Rt, based on ten-day changes in diagnostic test-positive rates:

  • July 22 — August 1:   8.2%/8.7% = 0.94
  • July 12 — July 22:   8.7%/7.9% = 1.10
  • July 2 — July 12:   7.9%/6.6% = 1.20
  • June 22 —  July 2:    6.6%/4.7% = 1.40
  • June 12 —  June 22:   4.7%/4.6% = 1.02
  • June 2 –  June 12:   4.6%/5.4% = 0.85
  • May 23 –  June 2:   5.4%/6.6% = 0.82
  • May 13 –  May 23:   6.6%/9.8% = 0.67

According to this metric, the Rt has restabilized. Covid hospitalizations too have flattened. If deaths continue to lag about ten days behind test-positives and hospitalizations, then over the next ten-day interval deaths will plateau at a rate around twice as high as June’s low ebb. If the plateau holds, then every ten days there would be 2 million new infections and 11,000 new deaths. By the end of the year 16 percent of the American population will have been infected, with the covid death toll having reached 320 thousand.

That’s assuming steady state. The recent downward trend might continue into a contagion rate below 1, in which case new infections and deaths will begin slowly diminishing again.

On the other hand, schools reopen this month…

 

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