Post #1400, Part 1: Omicron and luck

Posted on January 22, 2022


This is the first of what I expect to be three posts, trying to look past the peak of the Omicron wave.

These next posts aren’t going to very cheery, so let me gratuitously toss in this graph of how well the U.K. is recovering from its Omicron wave.  In the past two weeks, they’ve gone from 200K cases per day to 80K.

Source:  Google.

There is a light at the end of the tunnel.  We might even see the same sort of rapid decline in cases here in the U.S., once we’re past our peak.

That’s enough good cheer for the time being.  Now it’s back to business.

Will we ever admit how lucky we were, with Omicron?

We dodged a bullet with Omicron.  I’m wondering whether anybody of importance is going to admit that.  And, maybe even have some intelligent discussion about what that means going forward.

Omicron produced much less severe illness, on average, than the prior strain (Delta).  But that was entirely a matter of luck.  If the roll of the genetic dice had turned out differently, we’d be filling mass graves now instead of sending our kids back to school and trying to get on with life.

Why?  As I understand the theory of it, ability to spread is more-or-less the only significant determinant of which variant of COVID becomes dominant.  This is almost by definition. The virus succeeds by spreading.  The better it is at infecting people, the more successful it is.

  • The Alpha (British) variant was about 1.6 times as infectious as the native (Wuhan) strain.
  • The Delta variant was again about 1.6 times as infectious as Alpha.
  • Omicron is maybe 3 times as infectious as Delta.

All other characteristics of a new successful variant are essentially chosen at random.  They are whatever-happened-to-occur on the virus whose mutations made it the most infectious of its generation.  They are the random hitchhikers on whichever ride is fastest.

I want to emphasize that what I just said isn’t just the opinion of some random blogger.  It’s  mainstream scientific thinking on how viruses evolve.  The popular notion that diseases must  get “weaker” as they evolve dates back to the 1800s, and has been “soundly debunked”, per this reporting, (emphasis mine):

As evidence mounts that the omicron variant is less deadly than prior COVID-19 strains, one oft-cited explanation is that viruses always evolve to become less virulent over time.

The problem, experts say, is that this theory has been soundly debunked.

Or, if you prefer a quote from an actual science publication, try this one, (emphasis mine):

“There’s this assumption that something more transmissible becomes less virulent. I don’t think that’s the position we should take,” says Balloux. Variants including Alpha, Beta and Delta have been linked to heightened rates of hospitalization and death — potentially because they grow to such high levels in people’s airways. The assertion that viruses evolve to become milder “is a bit of a myth”, says Rambaut. “The reality is far more complex.”

The upshot is that evolution breeds successful new COVID-19 variants based on their ability to spread, but the virulence of a successful variant is totally random.  As long as most of those who are infected can walk around for a few days infecting others, what happens after that is irrelevant.  Absent an Ebola-like mortality rate, there’s no strong evolutionary pressure on virulence one way or the other.

What if we’d had a different roll of the dice?

Consider where we’d be if Omicron had merely had the same average severity of illness as Delta.   Again, just by chance.

In the U.S., we’ve reached the point where daily new Omicron cases are five times the level seen at the peak of the Delta wave:

If Omicron had the same case hospitalization rate and ICU use rate as Delta, and our behavior did not change, we would have already filled about three-quarters of all U.S. hospital beds with Omicron patients.  More to the point, we’d have filled 150% of U.S. ICU beds with COVID-19 cases.  If we had combined Omicron’s case count with Delta’s severity, we’d have run out of ICU beds a couple of weeks ago.

Source:  Calculated from US DHHS unified hospital dataset.

To a close approximation, the only reason that didn’t happen is chance.  Just plain dumb luck.  That’s all that stood between having a somewhat stressed-out cadre of U.S. ICU nurses, and mass graves for all the COVID-19 cases that needed an ICU bed but couldn’t get it.

But immune escape isn’t random at all.

I want to make just one more grim little point about COVID-19 variants.

The ability of a virus to spread occurs against a background of the existing immunity within the population.  If you’ll read the article cited above, there’s some hint that it is not merely by chance that Omicron is good at re-infecting those who had prior variants, and not merely by chance that Omicron is good at evading immunity established by existing vaccines, which themselves targeted those prior variants.  Those “immune escape” characteristics of Omicron are plausibly (though not definitively) a product of evolutionary pressures.

Just for a moment, consider where Omicron evolved:  South Africa.  In the province where Omicron first emerged, roughly 70% of the entire population had antibodies against the prior strains of COVID-19 (reference).  Omicron emerged in an environment that virtually required that the next winning COVID-19 variant be able to get past immunity to prior COVID-19 strains.

To be clear, that point isn’t just random fear-mongering.  Viral evolution to escape the immune system is part of mainstream scientific thinking.  Scientists were busily predicting the ways that COVID might achieve immune escape long before Omicron was on the scene (reference).

In South Africa, at some point in their Omicron wave, their government noted that about 8 percent of their Omicron cases were re-infections.  That was, at that time, unusual enough to merit notice.

And in the U.S.?  Near as I can tell, it’s starting to look the same.  The only state I know that had the foresight to track reinfections routinely is Missouri.  As of a couple of days ago, nearly 8 percent of infections in Missouri were re-infections (below).  That’s a radical departure from earlier periods, and so presumably that’s due to Omicron.


I want to put a little addendum on this, because the nut-o-verse has this fixed idea that “natural immunity” from infection is superior to what you can get from a vaccine.  So I want to be clear that these are re-infections, not breakthrough infections (infections of vaccinated individuals).  These are people who had recovered from some prior strain of COVID-19, and so had all the “natural immunity” that can provide.  And yet, they were infected all over again Omicron.

In any case, the striking re-infection rate that was noted in South Africa seems to be occurring in the U.S. as well.  And that’s probably not random at all.

On the plus side, I gather that, as with breakthrough infections of vaccinated individuals, re-infections tend to be milder than average.  Even if the virus can evade some parts of your immune system, other parts of your immune system remain primed to fight it.  As a result, a lower portion of individuals with breakthrough infection or re-infection end up with severe cases.

Summary of Part 1

To me, this good news / bad news story — Omicron’s combination of low severity and high infectiousness — reminds me of those times when NASA tells us that Earth just had a near-miss with some heretofore unknown killer asteroid.  I guess we’re supposed to feel good about that, compared to the alternative.  But a rational person can’t help but ask, “what about the next one”?

And that’s where I’ll end Part I