Post #1035: Herd immunity, part 1: Vaccines don’t matter, much, yet

It’s about time to revisit herd immunity.  So far, all I’ve been able to say, from the data, is that we’re not there yet.  (Duh.)

I’m going to start off this next set of posts by explaining why the current vaccinations don’t matter (much, yet) in terms of getting individual states or the U.S. as a whole to the herd immunity level. Continue reading Post #1035: Herd immunity, part 1: Vaccines don’t matter, much, yet

Post #1000: The simple arithmetic of the U.K. coronavirus variant

Today’s numbers.  Looks pretty good.

But not good enough.  They aren’t good enough, as they currently exist, to prevent a fourth wave of COVID, from the U.K. variant.

But don’t freak out just yet.  FWIW, my calculation is that if we merely stay the course — keep vaccinating at the current rate, maintain existing COVID hygiene — the inevitable spread of the U.K. variant will merely cause a slowdown in our recovery, and need not cause a fourth U.S. COVID wave.

Details follow.

Continue reading Post #1000: The simple arithmetic of the U.K. coronavirus variant

Post #991: New COVID cases per day, down 44% from the 1/8/2021 peak

Source:  Calculated from NY Times Github COVID data repository, data reported through 2/2/2021.

Just a brief reminder, because this gets next-to-no news coverage.

Peak-of-the-peak occurred 1/8/2021:  Rounded, that was 78 new cases / 100,000 / day (seven day moving average).

Currently, as of 2/2/2021:  Rounded, it’s 44, ditto.  Or a 44% reduction in new cases/ 100,000/ day. Continue reading Post #991: New COVID cases per day, down 44% from the 1/8/2021 peak

Post #990: Vaccine registration should not be this confusing

I just want to clarify a few things about registering to get the COVID vaccine, here in Fairfax County.  I did manage to register today.  I think.

And they sent me a text to confirm.  It said:

This is an automated message.  Please do not respond.  Reply with YES to confirm receipt.

That delightfully ambiguous message was of-a-piece with the rest of it.

Anyway, Fairfax County is now on phase 1b of vaccination.  That’s critical workers (police, teachers, grocery, mail, and so on), those age 65+, and those with health conditions putting them at risk of severe COVID.  You can find the full, detailed list at that “What is Happening” link on this web page.  It’ll probably be some months before they get through persons qualifying under 1b.

Continue reading Post #990: Vaccine registration should not be this confusing

Post #982: Herd Immunity IV: The simplified version.

Judging from the feedback I’ve gotten, most people can’t make head or tail out of my last three posts on herd immunity.  (Post #978, concept; Post #979, empirical estimate; Post #981, U.K. variant estimate).

At my wife’s suggestion, let me just tell it as a story, and see if that’s clearer.

You’ll hear that 70% of the population must be immune to COVID-19 before we can end the pandemic in the U.S. 

That’s wrong.   Or, at the very least, that depends on what you mean by “end”. 

By “wrong”, I don’t mean that there’s some uncertainty around that number.  There is, to be sure.  But by “wrong”, I mean the 70% figure is conceptually wrong.

If we’re talking about the problem we are facing right now — ending this current wave of the pandemic — then that’s the wrong number to look at.  It’s far too high.  And that’s because most people who use that 70% figure don’t have their thinking straight about what, exactly, that 70% number represents.

And, ironically enough, clarifying that last point was what those confusing posts were about.  So let me try to fix that with this post. Continue reading Post #982: Herd Immunity IV: The simplified version.

Post #979: The two distinct levels of herd immunity, Part II

Edit:  Read Post #982 first.

This post presents a calculation to match the herd immunity discussion of the just-prior post.  Read Post #978 first, then this one.

Here, I back-solve for the level of immunity in the population that should bring the effective COVID-19 viral reproduction factor below 1.0 (i.e., end the third wave of the pandemic), as long as we maintain masking, distancing, and other behaviors limiting viral spread.

This is a simple calculation, based on one point in the progress of the pandemic in North Dakota.  That point being the two weeks when North Dakota saw its sharpest increase in cases.

So there’s not a lot of accuracy here.  And it’s not an estimate, in the sense of being a statistic calculated from pooling a lot of data.  It’s really just a round-numbers (but data-based) illustration.  It shows that the two different herd immunity concepts defined in the prior post lead to two very different levels of required population immunity.  And that we may already be hitting the lower level in some states.

Bottom line:  40%.  Once something like 40% of the population has been infected, that ought to be enough to set the third wave of COVID on a downward trajectoryAs long as we maintain masking, distancing, limits on social gatherings, and other such controls.   But we’d still need the classic “70% herd immunity” to return to normalcy, meaning, life without those controls.

The upshot is that the uniformly downward trajectory seen in the U.S. Midwest probably isn’t a fluke, or luck.  It’s probably just a matter of arithmetic.

The clear policy implication is that there is a more efficient way to use the COVID vaccines, if the goal is to bring the U.S. third wave of COVID to a close.  You should concentrate vaccination in those states that have had the fewest infections so far.   You shouldn’t aim for an equal share of the population vaccinated in each state, as we are now.  You should aim for an equal share immune in each state, either via vaccination or via prior infection.  That means shifting vaccine from states that have already had widespread COVID infection, to states where a higher fraction of the population still lacks immunity to the virus.

Continue reading Post #979: The two distinct levels of herd immunity, Part II

Post #976: Simple projection to March 1, and herd immunity.

How close will the U.S. be to herd immunity for COVID-19, on March 1 2021?  Even with the significant uncertainty involved, it’s worth making a few simple projections of that.  If nothing else this will put the current vaccination effort into perspective.

Even under a rosy scenario where vaccine injections double from the current 1M/day, and new infections continue to fall, only about half the population will be immune to COVID-19 as of the start of March 2021.  That’s well below the 70% that was thought to be required for herd immunity under the original strains of COVID, let alone the higher percentage that will be required for the more infectious U.K. strain.

Why does March 1, 2021 matter?  If the U.S. COVID third wave truly has crested, our next test will come as the more-contagious U.K. variant becomes the dominant U.S. COVID strain.  That’s predicted to happen sometime in March 2021.  Near as I can tell, that prediction is based solely on the amount of time it took for that strain to become dominant in the London area.  So that amounts to a crude guess.  But, at present, that’s the only guess we’ve got.

And if that’s correct, then vaccinations should proceed as quickly as possible.  But under any plausible scenario, vaccination alone won’t prevent a fourth U.S. wave of COVID-19.  We really need to be thinking about what else we’re going to do — such as making N95 masks available to citizens — in addition to vaccinations.

Details follow.

Continue reading Post #976: Simple projection to March 1, and herd immunity.

Post #973: 50 million Frenchmen can’t be wrong?

Sometimes it seems like the U.S. has cornered the market on ideologically-driven foolishness.   So I always find it refreshing to hear of seemingly first-world* countries where fact-free stupidity has an even tighter grip on the population that it does here in the U.S.A. Continue reading Post #973: 50 million Frenchmen can’t be wrong?

Post #969: Political affiliation: Vaccine irrationality and its side-effects.

Every once in a while I stumble across separate pieces of seemingly-true data that make me question my own sanity.

When in fact, I should be questioning the sanity of others.


As I have noted before, flu vaccine is only about 60% effective in the best years.  Most years, it’s not even that effective.  (The graph on the left is from the U.S. CDC).  Flu rarely kills anyone other than the frail elderly, and has a case mortality rate of about 0.1% in a typical year.*  For most people, flu is a nuisance.  And most people have some degree of native immunity against some prevalent strains of flu, every year.

* That’s flu as cause of death, divided by flu “cases”, that is, people who were formally diagnosed with flu.  And that’s really the only hard number that exists, in this regard.  If you see somebody citing something else, either they’re making it up, or they are using a denominator that is something other than diagnosed cases.

In short, with flu vaccine, we’re talking about a modestly-effective way to reduce the odds of catching a mostly-harmless short-lived disease.  That you might not catch anyway, because you already have some of the right antibodies.

By contrast:  The COVID-19 vaccine is being touted as 95% effective.**  COVID kills a lot of people, and so far in this pandemic the U.S. case mortality rate rate is (400,000 / 24,100,000 =) about 1.6%.**  And near as we can tell, nobody has native immunity to COVID.

** As discussed in earlier posts, the COVID effectiveness can’t be directly compared to the flu effectiveness.  For COVID, that’s the effectiveness at preventing severe, symptomatic infections.  They don’t actually know how good the vaccine is at preventing infection in total (including mild and asymptomatic infection), because they didn’t draw blood and test for antibodies.  By contrast, the flu figure is the effectiveness at preventing all infections, as evidenced by presence of any antibodies to flu in the blood, whether or not flu symptoms were present.

*** See note above.  Anybody who cites a vastly lower number is either making it up, or using some other denominator such as an estimate of all infections.  In which case, the number would not be comparable to the 0.1% case mortality rate for flu.  You see a lot of disinformation based on apples-and-oranges comparisons between some putative “all infections” mortality rate for COVID, and the standard case mortality rate for flu.  That’s not a valid comparison.

So, COVID is more dangerous, the COVID vaccine is more effective, and fewer people have any immunity to COVID.  Compared to flu.  Those appear to be the facts.

And so, rationally, shouldn’t you be more willing to get the COVID vaccine than to get the flu vaccine?  I mean, maybe you just dismiss all vaccines.  OK.  But for the more rational part of the population, shouldn’t you be more likely to get the COVID vaccine than the flu vaccine, given the facts?

Nope.  Not if you’re Republican.

Here are results from two seemingly accurate national surveys.  And I note that the COVID question specifically phrased it as “determined to be safe by scientists and free to everyone”.  And that the December numbers were higher than estimates from September.  If you were to have asked in September, Republicans were far less likely to say they’d get the COVID vaccine than the flu vaccine.

For four-out-of-ten Republicans, getting vaccinated is off the table.  No matter what.  Not if the vaccine is guaranteed safe.  Not if it’s free.   You literally can’t give it away to that crowd.  Not even while the Republican POTUS is (incorrectly) taking credit for having developed the vaccine.

I’ve made up my mind, don’t confuse me with the facts?  That’s pretty much how I read this.  If that’s the attitude, then I guess there’s no arguing with it.  It is what it is, and it’s not going to change.  No matter what.

Luckily, screw ’em, we don’t need them.  They’re irrelevant.  Above is a modified version of the herd immunity calculation presented in a recent post.  The upshot is that if people simply follow through with their intentions, given the current state of the world, we’ll still exceed the 70% level required for herd immunity. And, as long as the limiting factor is the shortage of vaccine, it makes no difference that more than 40% of Republicans refuse to be vaccinated.  We’ll get there in the same amount of time, regardless.

So, ultimately, my take on it is, let them be ignorant.  It doesn’t do the population as a whole any harm, assuming that the overall amount of vaccine available is the limiting factor.  And assuming that 70% is the herd immunity level. (And that the vaccine literally prevents infections, including asymptomatic and mildly symptomatic infections, something that has not yet been shown.)  Even if we achieved no more herd immunity via infections, Republican intransigence on COVID vaccination is irrelevant.  We have enough rational people on both sides of the aisle to resolve this without them.