Post #1174: COVID-19 trend to 7/12/2021: Going vertical

Posted on July 13, 2021


On the plus side, most of the U.S. still has a low absolute number of new cases per day.

On the minus side, the increase in new cases is steep.

The most important thing to realize is that the infections shown at the end of the graph below occurred about 16 days ago, on average.  It takes about 12 days for the sequence of infection, symptoms, care-seeking, testing, and reporting to work out.  And then, this is a seven-day moving average of the reported data, so the numbers are, in effect, an average of another 3.5 days old on top of that.  The point is, you should add your best guess for 16 days’ additional spread in the community, beyond what you see here, as you consider any changes in your behavior in response to the fifth (Delta) wave of COVID-19 in the U.S.


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 7/13/2021, from”  The NY Times U.S. tracking page may be found at

A few comments

Keep in mind that we owe this current wave to the un-vaccinated.  Their collective decision to refuse vaccination means that they own this one.  You can try to dance around that all you want, but that’s the fact.

As a consequence, this near-vertical growth curve is being carried forward almost entirely by the roughly 40% of the population that is not fully vaccinated.

Source:  CDC COVID data tracker

And now, a few words about the numbers.

The near-vertical segment at the end of the line may look like the consequence of some data reporting errors, but it’s not.  I can say that because I expected to see it.  It’s a consequence of the intermittent data reporting by many states, combined with a rapid increase in the trend rate of growth.

I haven’t reported the trends for the past two days because there was no point to it.  Most states no longer report new case data on the weekend.  As of yesterday, for example, I only had current data on 12 states.  The rest were weekend non-reporters.

Given that non-reporting, I have to wait for Monday’s data, reported on Tuesday (today), to get a fresh look at the numbers.  And that’s what happened today:  all but a handful of states finally reported fresh case counts.

Bear in mind that I’m plotting a seven-day moving average.  With that, as long as all cases for the past seven days have been reported, it doesn’t really matter if the states report them in some “choppy” fashion.  The only time non-reporting is an issue is when it’s current — when the most recent observation for a state shows zero new cases.  When that occurs, I gap-fill any missing number with each state’s most recent seven-day moving average, from the last day on which the state reported data.  In essence, I assume the rate of new cases remains flat.  That gap-fill is then replaced the next time the state actually reports new case count data.

That big jump at the end of the line is an assumption a flat rate of daily new cases, colliding with reality.  The reality is that the new case rate was ramping up.  And we (mostly) caught up with that today.

As a consequence, the seven-day increase shown in the table is mostly true and correct.  It’s not overstating anything.

To the contrary, it’s actually a slight understatement, because a handful of states (including Florida) haven’t reported new data yet.  Once they report, and I replace my gap-fill with the actual data, the true seven-day increase for today will be higher than what is shown.

As a matter of completeness, I should also say that this is too soon to be some one-off consequence of July 4th celebrations.  Best guess, it takes an average of about 12 days for any new wave of infections to make it into the data.  Any impact of fresh infections due to July 4th celebrations won’t begin to appear until the end of this week.

Finally, we should start asking when the CDC is going to wake up this time.  It only took them what, about three months, and some public shaming by the head of the Chinese CDC (Post #590), before they advised U.S. citizens to wear masks.  It was damn near a year before they finally admitted that aerosol (airborne) transmission of COVID-19 was common (Post #1142).  At that rate, I guess by September or so maybe they’ll find enough backbone to be able to revise their most recent mask guidance, in response to the this Delta-drive fifth U.S. wave of COVID.

Here’s the issue:  You aren’t going to get the un-vaccinated to wear masks unless everybody wears masks.  My observation is that the only enforcement of mask use is by social norms.  If nearly everyone is wearing a mask, that (and only that) gets the message across that masks are required.  But if everybody has to wear a mask again, that means you have to ask vaccinated people to wear masks.  Which is a near-impossibility now because everybody tries to comply with CDC guidance.  And current CDC guidance that says that if you’re fully vaccinated, you can more-or-less go back to your pre-pandemic lifestyle.  No masks needed.  And that might even be true, from a purely scientific viewpoint.  But that’s now a huge barrier to putting a lid on this fifth wave, from a health care policy standpoint.  Current CDC guidance effectively bars the re-creation of social norms that enforce mask use in public places.

I don’t know whether it’s worth presenting any more analysis.  Right now, the absolute number of new cases is low.  But it doesn’t look like that’s going to true  for very long.

This fifth U.S. wave of COVID-19 was expected, based on the numbers (Post #1160).  It’s unfortunate that this one looks like it’s going to exceed expectations.