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.

Post #968: Vaccine strategy: Maybe we should try the boats first.

Source:  Clipart library.com

 

 

 

Last year, in 2020, when the Federal government called up the national guard to set up flu vaccine centers, I was a little surprised.  That, combined with the unprecedented mobilization of the United States Public Health Service to provide the needed medical personnel.  But what truly got my attention, last year, was when FEMA was tasked with retrofitting existing mass gathering venues to be used as Chinese-style mass flu vaccination centers.

Wait.  You don’t recall any of that?  Thank goodness, because neither do I.

But how on earth else could the U.S. have delivered 192 million flu vaccines in the last five months of 2020?  More than 100 million flu vaccines in the September and October alone, a span of roughly 60 days?

Was that some sort of miracle?

Nope.  It was business as usual.  It wasn’t even a particularly large number by historical U.S. standards. Continue reading Post #968: Vaccine strategy: Maybe we should try the boats first.

Post #959: If you’ve been vaccinated, do you still need to wear a mask?

If you’ve been vaccinated, do you still need to wear a mask?  I got this question from a reader a couple of days ago, and gave a partially-correct answer via email.  Here, I’m going to post what I believe to be the fully-correct answer.

Briefly:  Yes.  The CDC says you still need to wear a mask, social distance, and so on.  As long as the virus remains widely circulating in your community.  That’s not just the CDC being its usual fussy self.  There are sound reasons for that, involving non-trivial risk of catching and spreading disease.

In this post, I’ll try to explain that.  But, at the minimum, that “90% efficacy” you read about doesn’t include asymptomatic or mildly symptomatic infections.   They only counted severe, symptomatic cases.  The reduction in total coronavirus infections is unknown, and you can still spread the disease if you get a mild case of it.  In addition, that 90% reduction was based on all the participants maintaining their existing COVID hygiene.  If you get vaccinated, then start hanging around maskless in bars, you plausibly have greater odds of getting infected after the vaccine than you did before it.

But surely that has to prompt a few follow-on questions.  I’m not going to provide detail on these, in this post.  But I’ll give you my answers.

Well then, when can we  ditch the @#$@# masks?  I think the answer to that is “when the Governor says we can”.  We’ll get there when we get there.  I don’t think it goes any deeper that that.  It really shouldn’t be an individual-level decision, but that’s a topic for another post.

Continue reading Post #959: If you’ve been vaccinated, do you still need to wear a mask?

Post #899: Vaccine allocation rule is straight per-capita

Per this reporting from NPR, the initial doses of COVID-19 available in the US will be distributed across the States on a straight per-capita basis.  So I have to take back everything I said in Post #896.  Even if allocating on a per-capita basis isn’t the smartest way to do it, it certainly is transparent.

The reason this is straightforward may simply be a matter of arithmetic:  The number of doses they are talking about (6.4 million) is about enough to immunize half of US hospital workers (6.6 million, per the US Bureau of Labor Statistics), given that that these first two vaccines require two shots.

So, under these rules, Virginia should be allocated about 165,000 doses, which is enough to immunize just over 80,000 people.  At present, hospital employment in Virginia is listed as 165,000 (from the US BLS). That would not count (e.g.) physicians who have admitting privileges at those hospitals.

Bottom line is that allocation of the first round of vaccines is fairly uncontroversial, because it’s probably all going to be allocated to (and still not fully cover) hospital workers and similar high-risk front-line workers (e.g., paramedics, physicians).  It is unlikely to result in significant immunizations beyond that core group of health workers.

In short there’s really nothing to fight over, yet, regarding the allocation of vaccines to states.

Post #896: Has anybody seen our vaccine distribution plan?

Source:  weareteachers.com

I’ve seen it.  I think.  Such as it is.  Maybe.

Before I even try to be amusing about this, take a look at it yourself.  You can read it by following the links on this US DHHS web page.  This is the plan, as released in late September (.pdf).  And this is the “playbook” for executing that plan, released late October (.pdf).

The whole gist of the plan, such as it is, is that vaccines will be distributed through the States.  Presumably, via state public health departments.  You can see an outstanding summary of the status of those State plans via the Kaiser Family Foundation website.   It’s agreed-upon that certain vulnerable or critical populations will get vaccinated first, such as health care workers.  Beyond that, it’s up to the States to determine the distribution routes.

But now, turn to the key table in the Federal plan showing how the vaccine doses will be divided up among the States.  Our allocation plan, as part of the overall distribution plan.  And you will soon find that there is no such table.  Continue reading Post #896: Has anybody seen our vaccine distribution plan?

Post #892: Moderna’s COVID-19 vaccine appears effective.

Today Moderna announced that its COVID-19 vaccine is 94.5 percent effective.  As with the Pfizer announcement earlier, it’s hard to tell exactly what that means.  But, based on the article cited just above, it appears to be 95% effective in preventing disease severe enough that the infected person sought medical treatment and was tested and found to have COVID-19.

This is based on a total of five COVID-19 cases diagnosed among persons vaccinated, versus 90 among the placebo (non-vaccinated) group in their clinical trial.

Up to now, no information suggested that the Moderna vaccine would be this effective.  And, certainly, their lack of track record (at ever having produced a successful vaccine) did not bode well for success.  Accordingly, I had assumed that Moderna’s COVID-19 vaccine would be just as (un) successful as all their prior attempts at making a vaccine.

I was wrong.

That said, I am still puzzling over an event that occurred two months ago. 

Two months ago, we got news that (some) vaccine sponsored by the US had just 70% immunogenicity.  See Post #815, dated September 16, 2020.  That is, just 70% of persons treated with the vaccine produced the appropriate antibodies against COVID-19.  That would have set an upper limit on effectiveness of no more than 70%, and set a likely effectiveness of (perhaps) 55%.

This was the episode in which the director of the CDC talked, on camera, about masks providing better protection against COVID-19 than a vaccine.  That was when he announced the 70% immunogenicity of (whatever) vaccine he was referring to.

The common assumption was that this was the Moderna vaccine.  I.e., both the Johnson and Johnson and Pfizer vaccines had published their immunogenicity data months earlier, per Post #827, and showed virtually 100% immunogenicity.)

Now that I look a little harder, I have no clue what the CDC director could possibly have been talking about.  By the date of that news conference, Moderna had also published its immungenicity data and showed high immunogenicity of its vaccine.

In any event, these results are not coming from the manufacturers, but from the Federal panel chosen to oversee the clinical trials.  So, absent some wacky conspiracy theory, we have to take them at face value.  Whatever-it-was that the CDC director was discussing two months ago is now just an odd and unexplained footnote.   As was the fairly common expectation among infectious disease professionals that the COVID-19 vaccines would be far less effective than the Pfizer and Moderna vaccines appear to be.

As a final footnote, you cannot compare the effectiveness of these vaccines, as stated, with the effectiveness of the seasonal flu vaccine.  The COVID-19 research is using a different measure than the flu vaccine research.  For flu, they count as failures all persons with any evidence of infection with flu at any point, based on antibodies found in their blood.  The “ineffective” flu cases include a significant fraction of individuals who were never sick with flu, and were only known after-the-fact to have been infected with flu, based on a blood test.  By contrast, the COVID-19 results appears to be based on counts of individuals who had symptoms severe enough to prompt them to seek medical treatment, and then to get tested for COVID-19.  Asymptomatic infections are never counted.  Because of that, the effectiveness measures for the COVID-19 vaccines will appear higher than the effectiveness numbers for the seasonal flu vaccine.