Post #1124: COVID-19 trend to 4/26/2021

Posted on April 27, 2021


If I had to sum it the current trend, it would be slow progress but no consistency.  For the U.S. as a whole, new COVID-19 cases per day continue to fall slowly.  But if you plot the individual states, there’s nothing approaching a clear, common trend across the states.

You can see that below.

(I’ve rebased these plots to start on 3/1/2021, just before the start o the U.S. fourth wave of COVID-19.  I’ve also added about 11,000 cases to New Jersey today, as they dropped roughly that many duplicate cases in their last day of data.)


Source for this and all other graphs of new cases:  Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 4/27/2021.  The NY Times U.S. tracking page can be found at

There’s a slight downward trend.  There is no new crisis area to take the place of Michigan.  If you plot the individual states, there’s no obvious downward trend that is visible to the eye.

Otherwise, it’s just business as usual. 

There are no outbreaks in the five states with the highest percentage of the U.K. variant.  But there’s also no particular downward trend either.

Cases continue to trend upward in Oregon and Washington.  Colorado is still an outlier among Mountain states.  The Northeast area is generally trending downward.  Basically, same as it has been for the past couple of weeks.

The elderly continue to get vaccinated, albeit at a slower pace than in the past.  Between these two snapshots, the vaccinated fraction of the elderly increased by just over 0.2 percentage points per day.  That increase is less than it was, say, four weeks ago.

It’s just a very odd time.  The vaccines are clearly working, but we can’t quite get to the point of shutting this down via herd immunity.  And it still looks as if we’ve passed a peak in our vaccination rate, although we won’t know for sure until use of the J and J vaccine picks up again.

Source: CDC.

What does the low rate of “breakthrough” infections reveal?

In a sense, the U.S. population now splits into two pieces:  Vaccinated and not.  New COVID-19 cases are almost unheard-of within the vaccinated population.  You can see rates reported at this link.  If I’ve done the math right, the reported rate of COVID-19 infections among fully-vaccinated individuals in Michigan works out to 0.2 cases / 100,000 / day.  Less than under one-hundredth the rate for the Michigan population as a whole, for that period.

That low rate shows that this is due both to medicine and to behavior.  Based on medicine alone (the vaccine randomized clinical trials), you’d expect to see one-tenth the number of infections.  I.e., the vaccines are about 90% effective in preventing infection.  But, in fact, you are seeing vastly fewer infections than that.  Plausibly, that’s because the people who are getting vaccinated are mainly those who have been taking this pretty seriously all along, and are not taking infection risks.

That low rate of “breakthrough” infections is good news.  But it means that essentially all the cases you see reported are from the shrinking slice of the population that has not been vaccinated.  And, by inference, increasingly contains people who aren’t being careful about COVID-19 hygiene.

So, for example, CDC reports that 81.7% of the elderly are vaccinated (shown above).  And yet, separately, they report roughly 7 cases / 100,000 / day for the elderly.  (Shown below as roughly 50 cases/ week.)

Source:  CDC

But this means that, roughly speaking, that’s 7 cases per day among the 18.3 percent of the population that hasn’t been vaccinated. Or a rate of nearly 40 infections / 100,000 /day in the remaining un-vaccinated elderly population.  If they were a state, the un-vaccinated elderly would rank second only to Michigan in terms of their current incidence of COVID-19.

And so, I think this needs to be said plainly.  Given the miniscule rate of “breakthrough” COVID-19 infections, the entire pandemic is being perpetuated by the increasingly small fraction of the population that won’t get vaccinated and won’t take COVID-19 hygiene seriously.

I’m now fully vaccinated.  And yet, I’m still wearing a NIOSH-certified N95 mask when I go to the store.  Not because I’m paranoid, but because I’m smart enough to calculate the odds and do the cost/benefit calculation.  I’m going to have to keep wearing a mask until the incidence in the community is far lower than it is now.

The more people refuse the vaccine, the longer it’s going to take to end this in the U.S.  And so, in a sense, the well-being of the many is held hostage by the stupidity of the few.  That’s not going to change until we finally have enough people immune, either via vaccination or via infection.  All we can do is wait for that to play out.