Post #1175: COVID-19 trend to 7-13-2021

Posted on July 14, 2021


New COVID-19 cases are up 92% compared to one week ago.  That increase was so hard to believe that I took the raw data and calculated the rates for a few states by hand.  Just to double-check.

What put it over the top, compared to yesterday, is that Florida finally reported fresh data, coming in with a seven-day moving average of over 27 new cases / 100,000 / day.  That’s higher than Missouri, which was, at one time, the epicenter of the U.S. fifth wave.

It really says something, I think, that we’re still setting new records more than a year into the pandemic.  I checked the data all the way back to April 2020.  That 92% increase is the largest one-week percentage change in new U.S. cases since the start of the pandemic.

And yet, we are still sleepwalking into this U.S. fifth wave of COVID-19.

Source for this and other graphs of new case counts:  Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 7/14/2021, from”  The NY Times U.S. tracking page may be found at

CDC remains MIA

I’m not quite sure how to describe the reaction of our Federal public health bureaucracy to this sharp turnaround.  Sleepwalking?  Autopilot?  Whatever it is, the lack of action by CDC is forcing states (such as California) to go it alone in revising COVID-19 hygiene guidelines.

So now we’ll get to see the extent to which the CDC actually bases its guidance on objective rules.  Or whether they just kind of make it up as they go along, or are simply so burdened with bureaucratic inertia that they are organizationally incapable of making a decision in a real-world time frame.

On May 13, 2021, the CDC decided that the COVID-19 situation in the U.S. was safe enough that vaccinated people could drop their COVID hygiene.  On that date, the CDC changed its guidance to say that fully-vaccinated people didn’t need to wear masks or practice social distancing when they got together.  And you may recall that the Director of the CDC cheerfully announced that change out of the blue, with no warning given to state public health officials.

Logically, then as the risk of infection rises back above the level that prevailed on May 13, 2021, the CDC should reverse its guidance.  Not that I expect it to.  But this gives us an excellent test whether or not the CDC’s guidance is actually based on an objective rules at all and/or whether the CDC is capable of changing its mind as the facts change.  Or whether, by contrast, they just make it up as it suits them or are so hidebound that it takes months to make a simple decision.  For sure, it makes absolutely no sense for the CDC to cling to that May 13, 2021 guidance if the situation changes materially for the worse.

The situation on 5/13/2021 looked like this:

  • The prevalent strain of COVID-19 in the U.S. was the Alpha (U.K.) strain, with an estimated r-nought (basic infectiousness) of about 3.3.
  • The seven-day moving average of new cases in the U.S. was 11 new cases per 100,000 residents per day.
  • The trend in daily new cases was slightly down.

The situation as of 7/13/2021 looks like this:

  • The prevalent strain of COVID-19 in the U.S. is the Delta (Indian) strain, with an estimated r-nought (basic infectiousness) of about 5.
  • The seven-day moving average of new cases in the U.S. is 8 new cases per 100,000 residents per day.
  • The trend in daily new cases is sharply up.

Even if you adopt the stupidest, simplest rule — we must be below 11 new cases / 100/000/ day — the CDC has maybe four days before the daily new case count rises above 5/13/2021 level.

If you were a little smarter about it, and factored in the greater infectiousness of the Delta strain, then the CDC should have already reverted to the prior guidance.  Compare the product of r-nought and daily incidence on 5/13/2021 (3.3 * 11 =~ 36) to the same quantity today (5 * 8 = 40).  The risk of community-acquired infection is higher now than it was when CDC issued its relaxed COVID-19 hygiene guidance on May 13, 2021.

And if you had a lick of common sense, you’d notice that the new case growth is extraordinarily high.  You’d realize that in today’s data, you’re looking at infections that actually occurred an average of about 16 days ago.  And you’d realize that if anything like the most current rate of growth has been maintained in the interim, the risk of community-acquired infection is vastly higher now than it was on May 13, 2021.

In other words, if the CDC actually did have some objective rule based on estimated risk of infection, the odds are overwhelming that we’re now on the wrong side of that rule.  By any reasoned estimate, risk of infection is now higher than it was when CDC relaxed its guidance.

Should I even mention that the prevalent vaccines in the U.S. were estimated to be 95% effective against the prior strains, but only 88% effective against the Delta variant?  If you calculate the relative risk of infection using the full chain of events, for a vaccinated individual the risk of infection is (1-.88) * 40 = 4.8 now, versus (1-.95) * 36 = 1.8 on May 13, 2021.  After accounting for incidence in the population, infectiousness of the variant, and reduced vaccine efficacy, we’re already at the point where risk of symptomatic infection for a vaccinated individual is well over twice what it was on May 13, 2021.

All we can do now is wait to see how long it takes for the CDC to wake up.  Just start marking down the weeks that pass until the CDC reverts back to the pre-May-13 guidance.  If it ever does.