Post #1173: COVID-19 trend to 7/9/2021: Yikes.

Posted on July 10, 2021


I looked at the most recent counts of new COVID-19 cases and immediately tried to identify data reporting issues.  I found none.  These appear to be real.

As you can see above, daily new cases increased by 29 percent over the past week.  I’ve drawn in the trend line so that you can see this isn’t based on the artificially low “dip” following the 4th of July holiday.  This seven-day period spans Friday-to-Friday, July 2 to July 9.  If anything, based on the data reporting around the Memorial Day holiday, it may take another few days before we see the full extent of the increase in cases.

I’m not into hyping the dangers of this.  But, as outlined in Post #1160, the numbers are against us on this one.  This new variant is significantly more infectious than the current variant and more resistant to vaccines.  That combination immediately moves us much further from herd immunity, making us more susceptible to fresh outbreaks.  As laid out in Post #1160, that combination also means that, practically speaking, it will be impossible to achieve herd immunity against the Delta variant.

That’s why, as this U.S. fifth wave got started, every time we’d get another day of low new case growth, I’d hedge my bets.  Along the lines of “the numbers and the theory still suggest we ought to be having a larger outbreak. So, maybe it’s just a matter of time.”

Looks like maybe it’s now time.

Deja vu all over again

And now, hilariously enough, we must all put on a straight face and solemnly ask: “Will American citizens respond to this change in a rational way?”

Oh, come on.  Seriously?

I’ve already seen one issue arise a half-dozen times.  If you want get the un-vaccinated into masks again in public, you have to ask everybody to wear a mask.  Not as a matter of science, but as a matter of social behavior.

To a close approximation, nothing and nobody enforces mask use other than social norms in an area.  Which means that, as a practical matter, if you want to get the masks back on, for the U.S. fifth wave, you have to see masks on all the faces.  And as a byproduct, yes, you have to ask vaccinated individuals to wear masks again.

Every time this has happened so far, the usual cast of idiots has had a field day.  That starts with the mainstream press, which inevitably reports this as “state mandates that vaccinated individuals wear masks”.  Which is true, but which completely misses the point, which is that states must ask everyone to wear a mask if that request is to have any hope of being effective.  This is immediately followed by all the anti-mask/anti-vaccine/anti-COVID-hygiene crowd, who say that asking vaccinated individuals to wear masks has no basis in science/is just Big Brother controlling lives, and so on.  Which is not exactly true (masks continue to reduce likelihood of infection even for the vaccinated), but is close enough to resonate with most.  But which once again completely misses the point, which is, once again, that to get the un-vaccinated into masks, the social norm must return to seeing masks on everyone.

I’m trying to get some amusement out of what will now predictably ensue, but it just ain’t funny.  At this point, going back to pandemic-hygiene rules because a sizeable minority can’t be bothered to get vaccinated just has no humorous aspect to it. 

Fact is, it’s going to be a pain in the ass.   A pain that we owe not to our own behavior, but to the behavior of the uncooperative and the ignorant.

And for the first time in this pandemic, I’m thinking that maybe I just won’t cooperate.  I’ve played by the rules and then some, from the outset.  My family is fully vaccinated, and we got vaccinated at the earliest opportunity.  I’m still cautious in indoor public spaces, and my only real (but small) exposure risk is from going to the gym, where by my calculation the health benefits far outweigh the COVID-19 health risks (Post #1163).

And now, in this totally unnecessary fifth U.S. wave, if a third of the U.S. population wants this to be a Darwin Test, then so be it.

Source:  The Circumlocution Office.

The only thing that brings me back from this stance is the under-age-12 population, for whom no vaccine has yet been approved.  Vaccinated individuals can get infected and spread COVID-19, although the likelihood of spreading it, upon infection, is low.  (I have not seen any quantitative estimate of how low.)  And so, if you fail to comply with COVID-19 hygiene mandates because you’ve been vaccinated, you are being an anti-social butt-head.  You have a chance of unnecessarily playing a small, not-clearly-quantified role in transmitting the disease to a truly innocent victim, because you are too precious to wear a mask and obey the rules.

So it’s not a pure Darwin Test after all.

If the Governor says to wear a mask, I will, and I won’t whine about it.

Deja vu all over again

I think we’re seeing both the impact of the Delta variant, and a repeat of the U.S. second wave.  The second wave was the summertime uptick in hot-climate states attributed to more time spent in dry, indoor air-conditioned air.  (To understand why humidity matters, see Post #895, then Post #894).

This isn’t true deja vu.  The situation now is not the same as it was last summer.   But it’s hard to say whether it’s better or worse.

On the plus side, we have a lot more people who are presumed to be largely immune to COVID-19.  That consists of the vaccinated, plus those who have recovered from infections.  But keep in mind that because the vaccines are less effective against Delta, that immune number might not be as high as you would think.

On the minus side, the Delta variant is vastly more infectious than the variant that was prevalent last summer.  The “r-nought” for the original COVID-19 strain in the U.S. was estimated to be around 2.5, while the same figure for the Delta variant is estimated to be 5 or higher.  (That’s the number of people that any one infected individual would go on to infect, on average, if no other measures were taken to prevent spread of infection.)

On the minus side, all COVID-19 hygiene has been dropped.  Near as I can tell, there’s not a state in the U.S. that has any restriction on public gatherings of any sort, hours of operation of bars and indoor restaurants, mask mandates, social distancing mandates, or any of the rest of it.

Is it worth grinding that through a spreadsheet to see what the plausible outcome of this is?  There are so many unknowns, but sometimes a little calculation is better than nothing.

Let me return to the type of calculation I did back around Post #979 That is, calculate the effective (observed) rate of new infections (R-effective) based on the initial rate (r-nought) and the factors in place that interrupt infections.

I’m going to do this quickly, for myself.  If you can follow along, that’s great.  Mostly, it’s not worth much because it embodies a lot of imprecision as well as some fairly arbitrary assumptions.  But here goes.

The basic equation is as follows:

R-effective = R-nought*(1 – infections blocked by some means).

That’s pretty easy to understand.  The number of new infections you actually get, from each infected person (R-effective) is the number you’d get with no precautions (R-nought), less the infections that you managed to block.

You have two main factors that block infections:  Immunity and COVID-19 hygiene.

I can rewrite that equation to include both the effect of immunity and COVID-19 hygiene, but I have to take out some estimate of the overlap of the two to avoid double-counting.  I use a simple assumption that COVID-19 hygiene measures were used at the same rate by everyone.  That yields this equation:

R-effective = R-nought*(1 – (immunity + hygiene impact – immunity*hygiene))

First U.S. summer wave, 2020.

  • R-nought 2.5.  In August 2020, we were still facing the original COVID-19 variant.  It had an estimated R-nought of about 2.5.
  • Immunity:  6%.  As of August 2020, the U.S. had 5 million confirmed COVID-19 cases.  Given how spotty testing was at that time, that probably translates to something like 20 million actual cases, or about 6% of the U.S. population.
  • Hygiene factor:  0.53.  For what it’s worth, I used actual trends at the time to infer the impact of all the COVID-19 hygiene that was in place at the time, as shown in Post #979 and others.

R-effective = 2.5*(1 – (.06 + .53 – (.06*.53)) = 1.105

But because it takes about 4.5 days for each new generation of infections, that R-effective translates into a 16 percent per week increase in cases.

U.S. current summer wave (2021), the Delta wave.

  • R-nought 5.  We’re now facing the Delta variant, and the smallest R-nought estimate I’ve seen for that is 5.
  • Immunity:  59%.  I went through this calculation in Post #1160.  That’s a rough cut, and embodies a lot of assumptions, but it’s the best number I’ve got.
  • Hygiene factor:  ??.  Near as I can tell, just about all restrictions on public gatherings have been dropped.  But about 40% of people across the U.S. still report that they wear masks in indoor public spaces. So, something materially less than 40% of the prior factor.

Mask use as of end of 2020:

Mask use currently:

Source:  Carnegie-Mellon University CovidCast.

Let me try a few values for the impact of hygiene:

The first column is a reasonable replication of the summer 2020 wave.  That combination of the less-infectious original variant, full COVID-19 hygiene measures, and a small fraction already immune should have resulted in a moderate 17% per week increase in daily new cases.

The second column shows what you would expect with current circumstances if we continued all of our COVID-19 hygiene measures.  The combination of the more infectious variant, full COVID-19 hygiene, and a much larger fraction of the population immune would yield a small 2% per week increase in new COVID-19 cases.

In the third column, note what happens when you introduce this more-infectious Delta variant, and drop half of your hygiene measures.  You get an explosion of cases.  Daily new cases would be doubling every week.

Although this is obviously crude, I think there’s enough content here to allow some pretty clear conclusions.

First, the existing level of immunity in the population is not nearly enough to counteract the higher infectiousness of the Delta variant.

Second, absent a return to strong COVID-19 hygiene measures, there’s a real potential for very rapid growth of new cases in the U.S. fifth wave.

Take that for what it’s worth.  As I keep saying, the numbers are against us on this one. 

Great Britain was in a fairly tight lockdown through most of the spread of the Delta variant there.  And they still ended up with a significant increase in daily new cases.

But the U.S.?  We’re sleepwalking into this next wave.  We have no formal COVID-19 hygiene in place now.  Anything we have is a remnant carried on by individuals who voluntarily wear masks and so on.  The CDC says it’s fine to resume your pre-pandemic life, no mask needed, if you’re vaccinated.

Right now, new case counts remain low in most places, and there’s really still only one area with crisis-level hospital occupancy rates (southwestern Missouri).

It’s difficult to make predictions, especially about the future.  But based on how the numbers shake out, I’d say this is a fairly risky situation.

Let me put it this way.  We don’t have anywhere near a large enough immune population to control the Delta variant by immunity alone.  And we aren’t doing anything else to control it.  All of this, at a time of year when an outbreak is likely anyway in the areas of the country with heavy air-conditioning use.  What, exactly, should we expect to happen under those circumstances?