Post #901: Maybe ND really has achieved herd immunity.

Source:  NY Times Github data repository, data reported through 11/27/2020.

This is one of those seemingly simple 2+2=4 analyses.   In this case, it’s literally 8*10 > 70.

The arithmetic isn’t rocket science.  Anybody can do that.  My only value-added here has been in keeping an eye on the situation, and realizing why that arithmetic might matter.

Right now, 10% of the population of North Dakota has been formally diagnosed with COVID-19.   As of data reported through 11/27/2020, they’ve had 77,242 known cases.  That’s out of a population of about 760,000 (per the US Census Bureau).  Or (77,242/760,000 = ~) 10%.

A 10/25/2020 publication by CDC staff says that, best estimate, on average, 8 people have had COVID-19 for every one that has been diagnosed. 

IF CDC staff are right, and IF that US average applies to the US Midwest, then North Dakota has probably achieved COVID-19 herd immunity.  Or is close to it.  And much of the US Midwest has or will be following suit in the near future.

Obviously, that’s two big ifs.  But anybody can follow the math.  That’s 8*10% = 80%, and that’s higher than the 70% conventionally thought to be required to achieve herd immunity to COVID-19.

Oh, and note the peaks on all the curves at the top of the graph above.

Discussion follows.  This brings together several points that I’ve brought up over the past two months or so. Continue reading Post #901: Maybe ND really has achieved herd immunity.

Post #900: Peak of the third wave: Is “dynamic herd immunity” capping the rate of spread of COVID-19?

Source:  Data from NY Times Github data repository.  Data reported through 11/23/2020.

An odd thing has been happening, even as the news is dominated by the worsening of the third wave of the pandemic nationally.  That third wave of US COVID-19 appears to be cresting in the states that led it.  And the strange part is that simultaneous crest across several states has nothing to do with any actions recently taken (or not taken) by state governments to contain the virus. 

The mere fact that some hard-hit states appear to have peaked, in terms of new COVID-19 cases per day, is not the odd part of this.  Here’s what’s odd.

First, note that several states peaked at just about the same time.  Within, say, a week of one another.  Two states peaking in the same week could be a coincidence.  But six or seven states?  Spanning more than 1000 miles?  All of them with extremely high rates of new COVID-19 cases per day?  It’s hard not to think that there’s something that ties that together.

Second, note that this peak occurred despite some states taking action and others not. Famously, for example, the governor of South Dakota refuses to institute a mask mandate or take other protective measures.

Third, note that these peaks occurred well before we could plausibly expect to see any results of any state actions, in any case.  For example, ND and IA mask mandates were passed 11/14/2020 (Post #890) and 11/17/2020 (Post #893), respectively.  Any reduction in infections that result from those changes could not possibly appear in the data prior to the end of November.

That’s due the “pipeline” of cases that are already infected, at any point in time, but haven’t yet appeared in the numbers.  It takes, on average, in most areas, about 12 days for any change in infection rates to appear in the data.  (That’s about five days from infection to onset of symptoms, and then another 7 on average for seeking medical attention, getting tested, and having the test results appear in the data).

Meanwhile, three other states in that vicinity have high case rates and continue with a relatively steep upward trajectory.  But all are well below the peak demonstrated by ND.

Finally, I need to supplement the above with one chart of states that got covered up in the tangle of lines above, and then the remainder of that block of states.

Note that, in particular, MN appears to have peaked in the last week.

And when I put that all on one map, it looks like this.  The block of green-ish states are those that a) had high rates of new cases and b) all appear to have peaked in the past, oh, week or so.  The red-ish states are those, in the same area, with high rates of new COVID-19 cases, but where trends continue upward, with no evident peak or leveling-off of new cases per day.

All pandemics are local.  And by that I mean that you’re going to be reading news articles about individual cities, within those states, that are running out of hospital beds.  And will continue to do so for some weeks.  But in terms of total cases within the states, for some reason, almost all of the states with extreme new-case loads decided to do a 180 in the past couple of weeks.  All in the same geographic area.  All at the same time.

Speculation on what might cause this.

First, let me be clear, I have no firm idea on what is causing this.  I just noticed the oddity, that’s all.

1:  Maybe it’s the weather, and so this break is temporary.  I note that this area had a heat wave just about weeks before these states started peaking.  That should have temporarily raised indoor relatively humidity, and if humidity is key to transmission (Post #894), should have slowed transmission.  And so, maybe this isn’t a peak, but it’s just a temporary break in the trend, due to that past weather event.

The problem there is that the heat wave affected all of those states.  Here’s Bismark, ND and Cheyenne, WY.  Pretty much the same weather pattern across both areas.  If it were solely an artifact of weather, we’d see a break in the trend for Wyoming.  Which we do not.

2: Maybe people wise up before their state government does.  The high incidence of COVID-19 in these states was public knowledge.  Maybe there’s some common threshold of hard-headedness that people can get past, with enough news coverage of how dire the situation is becoming.  And so, these peaks are an artifact of enough people waking up to the situation and changing their behavior, in each state, to break the back of the upward trend.

But the sharp reversals of trend, and the tight synchronization, don’t really seem to fit with that.  At least, not to my eye.  This has the look of something far more mechanical or automatic, and less the look of (e.g.) the will of the people shifting in favor of mask use.

3:  Maybe this is how herd immunity works in this situation:  It generates a natural cap on the rate of spread, for a given set of underlying conditions.  We keep hearing that we need 70% of the population to be immune before we achieve “herd immunity”.  That’s the point where the pandemic dies out for lack of enough “infectable” people to maintain the chains of disease transmission.  But maybe herd-immunity-type effects also limit continued rapid spread.

Herd immunity is not going to be a smooth process.  It’s not as if you’re going to run right up to the herd immunity level, and then have the pandemic stop all at once.  Instead, as a smaller and smaller portion of the population is at risk of infection, presumably the rate of transmission would slow.

At this point, best guess, somewhere around a quarter to a third of the entire population of North Dakota has already been infected with COVID-19.  (See Post #889 for details.)  That’s the roughly 8 percent that had been formally diagnosed, as of mid-November.  Times some unknown multiplier to account for cases that were never diagnosed (asymptomatic individuals and individuals with symptoms mild enough that they did not seek treatment or diagnosis.)

I’m not familiar enough with the techniques used to model epidemics to say for sure, but I’d bet that having a third of your population immune to the disease is enough to put a crimp in the rates of spread.  It might not stop it, but it might plausibly prevent the highest possible rates of spread from occurring.  Except for the fact that COVID-19 spreads largely via clusters, you’d be tempted to say, well, at this point, a third of the chains of infection that used to continue are now being truncated by running into an immune individual.

The point here is that that maybe the basic arithmetic of this pandemic makes the rate of spread somewhat self-limiting. Once it reaches some high rate of new cases per day, for long enough, the rate has to go down due to the rapid build-up of surviving immune individuals.

Notably, the case mortality rate for COVID-19 is now quite low (e.g., about 1% in the Commonwealth of Virginia).  That makes the situation for COVID-19 materially different from that of the 1918 Spanish Flu. With this low mortality, if  COVID-19 tears through a population rapidly, then it rapidly builds up a large population of immune individuals. And that large population, while not enough to stop the pandemic from continuing to spread, may be enough to cap the rate of spread.  The very fastest rates are no longer feasible, because enough chains of transmission are being truncated.

If so, that’s very good news for my “reefer test” ( Post #888).  That means that the rates won’t continue to climb until you finally run out of potential victims.  Instead, for a given set of circumstances, you’ll see the rates all peak around the same point.  And the commonality of that peak occurs because you’ve built up enough survivors to “clog up the works” just enough to cap the rate of spread.

As a footnote, I’ll bring back an earlier version of the diagram above.  Oddly, note that the two peak summertime states both peaked at just about the same daily rate of new cases.  Despite being in completely different climates and locations.  That was for the air-conditioning-led summer outbreak.  And now, with what I’d call the heating-led winter outbreak, we’re kind of seeing the same thing.  Just at a different level of new cases per day.

(But that may just be reading too much into the data.  There was a spectrum of peaks in the summer outbreak.  Obviously, the ones at the top are all going to be near the top.)

4:  Does “herd immunity” really require 70% of the entire population to be immune.  Maybe you run out of risk-takers well before 70% are infected.

How about people like me, who are basically minimizing exposure already, scrupulous about mask use, and wearing an aerosol-filtering fitted mask when shopping (Post #780, Post #807).  Does herd immunity require 70% of people in my situation to be infected before the pandemic stops on its own?  Or, by dint of isolating myself, am I more-or-less irrelevant to the herd immunity calculation?

Let me put it this way:  A vaccine provides (we hope) 90% protection against being infected.  We count (90% of) the vaccinated population as part of that 70% in the herd immunity calculation.

But suppose that a good mask and careful behavior results in 80% protection against being infected.  What’s the difference, exactly, between that, and being vaccinated?  (In terms of the herd immunity concept.)  The vaccinated individual is assumed to be (more-or-less) permanently removed from the pool of persons who can be infected.  The mask-and-behavior person remains at risk of infection, regardless.  So there’s clearly a long-run difference — the virus can slowly “pick off” persons from the mask-and-behavior pool, but not from the vaccine pool.  But in terms of breaking the chains of transmission, in the short run, I’d say that those two routes to stopping spread of the virus are roughly equivalent.  One terminates 90% of the chains, the other terminates 80% of the chains.  So to speak.

And so maybe, at some point, the population of risk takers that is responsible for high rates of spread gets thinned down somewhat.  Not by mortality, but by becoming infected and so becoming immune.  And so, even if just a third of ND residents are immune, maybe that’s a lot closer to 70% of the risk takers.

If so, the rapid spread attributable to failure to take precautions might be self-limiting well before 70% of the entire population is immune.  Maybe, to prevent the most rapid spread, all you need is 70% of the risk-taking population.  And that might be a much smaller fraction than 70% of the entire population.

Best guess:  “dynamic herd immunity”.

These synchronized and rapid reversals of the upward state trends, for the states with high growth rates, suggest a mechanistic explanation, rather than a behavioral one.

For sure, it’s not a result of government action.  That’s been piecemeal, and in key states (ND, IA) occurred far too recently to account for the turnaround.

The weather is something that would affect a broad area.  But the same heat wave that plausibly might have resulted in the peak in (say) SD also affected states where a peak has not yet occurred, such as WY.

Having the populations of these states all “wise up” at the same time seems improbable, given how close the timing is.

My bet is that the rapid growth is self-limiting.  The virus leaves so many immune survivors behind, in such as short period of time, that it chokes off that very rapid growth.  So it’s not herd immunity (that disappearance of the virus) but instead a natural limit on the rapid spread.  Rapid spread can only go on for just so long before it (in effect) chokes on its own impact on the population.

Let me call this “dynamic herd immunity”.  That’s the idea that a high rate of spread can go on for just so long before it has to slow down.  And that it will slow down well before 70% of the population has been infected.

How long that high growth may continue, and how rapid that growth can be, will of course depend on underlying conditions.  In these mask-averse states with dry and cold winters, that can proceed much faster than it might in states with good mask use and milder climate.

Seeing all these states, all peaking around the same time, around the same growth rate, suggests that there’s something about the mechanics of epidemics at work here.  My best guess is “dynamic herd immunity”.  A high rate of new case growth chokes itself off, at some point.  The virus will still be spreading, but at a slower rate.  And if so, that’s very good news from the standpoint of running out of hospital beds.  Maybe the lower apparent severity of the average case (Post #897), and “dynamic herd immunity”, mean that we won’t have to fail the reefer test after all.  We’ll manage to get through this, despite ourselves.

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 #898: Quarantining your college student rationally. Or, should I lock my daughter in her room while I go grocery shopping?

This post is motivated by the need to bring my daughter back from college next week.  What I was wondering is, should we all be wearing masks in the car?  But more generally, what’s the standard protocol, quarantine-wise, for returning college students?

Seems like a fairly straightforward question.  Given that there are going to be millions of college students returning from campus to home in the next few weeks, it seems like there ought to be be some standard answer to that question.

Sure seems like it.  Ought to be.  But there ain’t.  Let me summarize what I found.

When I do the math, under the circumstances I face, the likelihood that my daughter is going to give me a COVID-19 infection is 1-in-30,000.  Over the same period, the likelihood that I would just pick one up, as an average member of the community, is 1-in-93. 

So, to answer the question in the title, it makes no sense to lock up my college-age daughter, while I continue to go grocery shopping. 

Unless that’s to protect her, from the risk of COVID-19 infection that I might be bringing home.

Want do the quick-and-dirty calculation for your own returning college student?  Based on the assumptions below (the student tests negative for COVID-19 and doesn’t pick up an infection while traveling home), the 1-in-X odds of  your student transmitting infection to you, X = 11*campus enrollment / new campus COVID cases in the last two weeks.  If they don’t have a negative COVID-19 test, then replace the factor of 11 with a factor of 3.

Continue reading Post #898: Quarantining your college student rationally. Or, should I lock my daughter in her room while I go grocery shopping?

Post #897: Preparing for a hard winter, #9: Recent COVID-19 trends in Virginia, cold spots as hot spots, and extrapolating to mid-winter

It has been more than a month since I tabulated the trends in new COVID-19 cases in Virginia.  It’s no secret that the trend has been up.  Here’s Virginia, in the national context, as of yesterday’s data reporting.

Record new cases, but not record hospitalizations or deaths.

Continue reading Post #897: Preparing for a hard winter, #9: Recent COVID-19 trends in Virginia, cold spots as hot spots, and extrapolating to mid-winter

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


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 #895: A few words on room humidifiers

Source:  That well-known font of medical knowledge, the American Society of Heating, Refrigerating and Air-Conditioning Engineers.  This is from the 2016 ASHRAE Handbook—HVAC Systems and Equipment (SI), Chapter 22:  Humidifiers.

I started to look up the standards, if any, for room humidifiers, and stumbled across the graph above in, of all places the AHSRAE HVAC engineering standards manual.  I thought that was such an odd coincidence, given my last post, that it deserved special mention here.  HVAC engineers start their discussion of calculations for humidifiers by summarizing the significant health implications of maintaining proper indoor humidity.  The impact of humidity on flu mortality was demonstrated experimentally, thirty years ago, on mice.  And, sure enough, 40% to 60% is the zone that prevented the most flu deaths.

And now, a few words on room humidifiers:

I hate them.  All types of them.  Each in their own separate way.

If you already own and use a humidifier or two, the opinions in this posting are probably irrelevant.  Either you’re satisfied with what you have, or you aren’t.  But if you’ve never bought a humidifier before, you might find a useful tip or two here. Let me get you oriented.

1:  There are no standards, so buy big.

2:  The humidifier is an appliance that increases household work.

3:  Noisy, dusty, stinky, and/or expensive:  Pick one or more.

Think of all the worst properties of every appliance you’ve ever had, and they come together in the average room humidifier.  There are no standards.  They are built as cheaply as they can possibly be built.  You fill them by hand, in any of several awkward ways, frequently.  In some cases, you need to clean them frequently, again by hand.  Some require using distilled water, others require you to dump poison in the water.  Replacement items are expensive.  And so on.

Over the years, I’ve tried more-or-less every type of humidifier there is.  I have grudgingly settled on a fixed-pad evaporative humidifier with use of bacteriostat (bacteria-suppressing solution).  In particular, my go-to humidifier is this one.   For reasons that I’ll eventually get to in this posting.


1:  There are no standards, so buy big.

Pretty much every humidifier on the market will tell you how many square feet it is capable of humidifying.  And if you think about that for even thirty seconds, you’ll realize that, whatever that number is, it’s not well-defined.

  • What outdoor temperature and humidity do they assume?
  • What ceiling height do they assume?
  • How leaky or tight is the construction being humidified?
  • What level of indoor relative humidity do they guarantee?
  • Is that the max output — do you have to run it on high all the time to get that?

And so on.  Let’s face it.  Something that will effectively humidify 1000 square feet of housing in Virginia is going to be inadequate for 1000 square feet in Bismark or Cheyenne.  So that one-size-fits-all rating has to be taken with a grain of salt.

If you look at an actual engineering discussion of humidifiers (as in the ASHRAE manual), you soon realize that the whole subject is pretty tricky.   It’s all about the amount of water that you need to put in the air, per hour, to maintain humidity.  And that’s affected by lots of factors and lots of limits.

Just to give one example, in colder climates, the type of window glazing sets an upper limit on how well you can humidify an indoor space.  Set the humidity too high, and the water simply condenses on the insides of the windows.  If it’s freezing out (32F), and you have single-glazed windows, you’ll get condensation on the windows if you try to maintain anything above 30% relative humidity.

Arguably, the single largest contributor to your humidification load is the number of air changes per hour for your home.  The air in your home is being continuously replaced with outside air.  The current US standard is that all the air in your home should be replaced at least once every three hours.  Most modern building codes aim for roughly one change every two hours.  A typical value for an older home would be one air change per hour.

If you have an older home, the upshot is that you need to re-humidify the entire air volume of your home, once per hour.  In a more modern home, that might be once per two hours, or even three hours.

Let me now do a little calculation to show you just how much water that might entail, in the dead of winter, in this area.  In January, in Washington DC, the average outdoor air temperature is 36F and the average relative humidity is about 61% (per this source).  Let’s say you have an older home, 3000 square feet, with 8′ ceilings.  And, finally, you want to maintain 40% relative humidity inside your home, at 68F.

Under those assumptions, you need to put 0.75 gallons of water, per hour, into the air.  Or 18 gallons per day.  Just to overcome that one air change per hour.  This doesn’t count moisture that literally escapes through the walls of your house.  But it also doesn’t count the modest amount of moisture added to the house by cooking, showers, and so on.

If you have a tightly-constructed modern home, you’d need far less.  Or a smaller home.  But if you have a bigger, older house, of the type described here, you need somewhere around that 18 gallons of water per day to maintain 40% relative humidity in the dead of winter.

You’d need four or five of  my go-to humidifier, running at top speed (four gallons/day), all day long, to maintain 40% relative humidity.  (Whereas, if I went by the rating on the box, I’d only need three. And I want to avoid running at top speed, due to the noise.)

The upshot of that is:  Think big, and buy a hygrometer (humidity meter) or two.  If you’re planing to humidify your entire house, buy somewhat more humidification capacity than you think you’ll need.  You can always turn the humidifiers down to a lower speed, if you don’t need that capacity.  But you will be surprised how frequently you will exceed your humidification capacity in the dead of winter.

It is possible to over-humidify a home.  Particularly if you have a modern, well-sealed home.  But if you live in an older home, over-humidification is tough to achieve unless you really go overboard.

2:  The humidifier is an appliance that increases household work.

I don’t need to belabor this, I think.  In the example above, that theoretical 3000 square foot older house needed 18 gallons of water per day.  That you, the homeowner would have to carry to the humidifier.  That’s 150 pounds of water, per day, carried by hand.  Inside your house.  Every winter day.

That gets really old, really fast.  Needless to say, Rule #1 is to locate any large humidifier near a source of water.

The only other thing to mention is routine cleaning.  If you have an evaporative humidifier, at a minimum, even if you put chemicals (“bacteriostat”) into the water, you have to inspect it weekly.  And take it apart and clean it every couple of weeks or so.  Maybe soak the evaporative pads to remove the mineral buildup.  And so on.

Just understand that it’s not like your other appliances.  Your other appliances, they reduce the amount of work you do.  Humidifiers increase it.

3:  Noisy, dusty, stinky, and/or expensive:  Pick one.

There’s no such thing as an inexpensive low-maintenance humidifier.  At least, not that I’ve come across, for humidifying a large area.

Cool mist humidifiers break water up into tiny droplets using ultrasound or some mechanical (“disk”) means.  They are quiet and reasonably energy efficient.  In my experience, they rarely have problems with mold or bacteria.

But 1:  But you’ll probably want to use distilled water.  And that’s expensive.  And environmentally unfriendly, for the energy required to produce and ship distilled water.  If you break down and use tap water, they produce mineral dust.  This is not just unsightly, it’s arguably bad for your lungs.  Some units have “de-mineralization” systems, allowing you to avoid distilled water, but I question the effectiveness of those.

But 2:  They are typically small, single-room units capable of producing no more than a gallon per day.  So if you’re of a mind to humidify your whole house, count the number of these you’ll need before you buy.  And every one of them will need to have the water reservoir filled periodically.

But 3:  In my experience, the interlock mechanism that keeps the water in the reservoir is tricky, fragile, and effectively impossible to replace.  It’s typically a spring-loaded contraption with plastic parts, and so is destined for the landfill one way or the other.

Warm mist (a.k.a.) steam humidifiers simply boil water.  They are quiet and you can typically use tap water.

But 1:  They are not energy-efficient.  You are literally using an electric resistance heating element to boil water, which is the least efficient and most carbon-intensive heat source you could choose.

Just as an example, boiling 18 gallons of water requires about 45 KWH of electricity/day, which would work out to about $200/month at $0.15/KWH.

(I could use an extras-for-experts here, because all the other humidifiers also use heat, but indirectly.  “Cool mist” isn’t a feature of the ultrasonic humidifiers, it’s an unfortunate and unavoidable side effect.  Without getting into the physics of sensible versus latent heat, cool mist (and evaporative) humidifiers more-or-less suck heat out of the air.  They require your heating system to work harder to maintain a given temperature.  Whereas warm mist humidifiers put that heat directly into the water at the outset.  So it’s not that warm mist humidifiers are inefficient because they require heat input.  They’re inefficient because they use a particularly inefficient heat source (resistance electric heat) for that heat input.)

But 2:  As with cool mist humidifiers, you’d be hard-pressed to find one capable of humidifying more than one small room.  So, as with cool mist, you’re going to need a lot of these if you’re going to humidify a house.

But 3:  As with cool-mist humidifiers, the interlock mechanism that keeps the water in the reservoir is tricky, fragile, and effectively impossible to replace.  The only exception is “baby humidifiers” where the electric unit just inserts into the top of the reservoir.

Evaporative humidifiers simply blow air over wet pad.  The air picks up moisture from the pad.  Some of them (“console” humidifiers) might have that pad in the form of a moving belt that dips down into a water reservoir.  Others have the pads fixed in place.  Some have to be filled (e.g.) by carrying pitchers of water to them.  Others have detachable reservoirs that can be filled at the sink, similar to cool mist and warm mist humidifiers.  You can use tap water with these humidifiers.  These are made in large sizes capable of humidifying several rooms.

But 1:  The use of a fan makes these noisy, particularly on their highest settings.  I’ve never had one that I would call “quiet”.

But 2:  These are prone to mold and bacteria problems.  You (IMHO) MUST use chemicals (“bacteriostat”) in the water reservoir to suppress mold.  You MUST inspect the pads weekly for any sign of growth.  You typically have to replace the pads at least once per heating season, at a cost of a few tens of dollars.  Barring that, you may need to take them out and soak them once per season to remove mineral build-up.  And it’s not a bad idea to empty these out and scrub the interior at least once per heating season, just to be on the safe side.

Summary:  What I use, and why.

Source:  Amazon.

I use the simplest, high-volume evaporative humidifier that I have found.  Because:

a)  I’m too cheap to buy massive quantities of distilled water.  That, and the size of the space to be humidified rules out cool mist humidifiers.

b) The inefficiency of resistance electric heat, and the small size of warm mist humidifiers, rule them out.

So I’m left with evaporative humidifiers.  The lesser of three evils.

The model I prefer has a few nice features.

First, few moving parts.  In particular, it has removable reservoirs for re-filling, but they have no mechanical seal mechanism.  Instead, they just sit on the humidifier the way a water jug sits on a water cooler.  And you “flip” them into place the same way you would put a jug onto a water cooler. It’s one of those bulletproof systems that is clever for its lack of cleverness.

Second, if forces you to look at the evaporative pads every time you refill the reservoirs.  So you can’t accidentally overlook mold growth, or skip required cleanings.  The pads are right where you can see them, all the time.

Third, all the electronics simply lift off, which makes it easy to scrub down the plastic base and sides.

When it comes to humidifiers, they are all made just as cheaply as they can be made.  In that situation, the less there is to them, the more robust they’ll be.  This is the least humidifier I could buy that gets the job done for me.

Post #894: Why is flu seasonal? Humidity and COVID-19 spread, final version

Source:  Graph from, original data from CDC Pneumonia and Influenza Mortality Surveillance.

Source:  Potential impact of seasonal forcing on a SARS-CoV-2 pandemic DOI: Publication Date: 16.03.2020 Swiss Med Wkly. 2020;150:w20224 Neher Richard A., Dyrdak Robert, Druelle Valentin, Hodcroft Emma B. Albert J.

This is a followup to Post #879 and Post #880.  It is, in fact, little more than an expansion of the literature review for Post #879.

Continue reading Post #894: Why is flu seasonal? Humidity and COVID-19 spread, final version

Post #893: Iowa governor implements mask mandate, and she did it before Iowa hospitals ran out of beds.

This morning I see that the Governor of Iowa has issued a mask mandate.  After some research, I found one thing about this change that is absolutely exceptional.  She did this, as far as I can tell, even though Iowa has not yet run out of hospital or ICU beds. 

That makes the governor of Iowa exceptionally forward-thinking relative to her Republican peers (see Post #890), for whom the norm is to act only when their hospital system has reached capacity.  For example, we have yet to see movement toward a mask mandate in South Dakota, which has far higher new infection rates than Iowa, and appears to have a similar level of slack in their hospital system at the moment.

But otherwise, the Iowa mask mandate fits the standard pattern for Republican governors (with apologies to cousin Larry).  Let’s see that this ticks all the boxes.

Freely and publicly disparaged mask used within the past month.  Check.  The governor of Iowa apparently called face masks a “feel good measure”.

All of that history goes down the memory hole, with no mention of it, let alone any apology for it.  Check.

Grudgingly implemented a weak mask order.  Check.  This one applies if you are indoors and will be at less-than-six-foot-distance from others for 15 minutes or more.  So, it doesn’t really apply to (e.g.) just going to the store, I guess.  And more-or-less any venue that can maintain six-foot distancing remains open.

Limited duration, as if this is all going to be over in a couple of weeks.  Check.  This one lasts just over three weeks, to December 10.  That’s the shortest I’ve seen so far.  And the clearest exercise in wishful thinking.

No means of enforcement.  Check.  Near as I can tell, the only entity mentioned was the Iowa Department of Public Health.  So, as with Virginia’s initial mask mandates, any enforcement would be on establishments (such as bars), not individuals.  For sure, there is no mention of penalties or fines for failure to comply.

Exempted any sort of religious service.  Check.

Included all the usual suspects such as closing restaurants and bars early, limiting the number of people in gatherings, and so on.  Check.

In a novel twist, high school and college sports are exempted.  In fact, pretty much every activity you can think of may continue, as long as people are six feet apart.

Those points are based on reporting in today’s Washington Post and a local Iowa news agency., as well as the proclamation itself.  You can read that here (.pdf).

As crazy as this sounds, I just don’t think they’re taking this very seriously yet.  What stands out clearly is the total lack of acknowledgement that aerosol spread might occur.  For example, you can still go to the gym and (e.g.) work out on a treadmill, so long as your treadmill is at least six feet away from the next one.

I mean, I guess this is better than nothing.  But if I were to follow those rules, here, I’d never wear a mask anywhere.  I can get all my shopping done without standing within six feet of another customer for 15 minutes or more.  Near as I can tell, in Virginia, these rules would amount to not having a mask mandate.  Add in a high level of non-compliance with what little restrictions this embodies, and it’s hard to imagine this could have much material effect.

And so, you come back to the question of what it will take, to make these folks take this seriously.  If ever.  And I come back to the same answer:  Bodies stacked in refrigerated trailers (Post #888).  So for the time being, all I can do is keep an eye out for the first failure of that criterion.

In the meantime, I guess I need to write up the relationship between humidity and flu season in temperate climates.  Again.  Because it sure seems like either all of the modern scholarly literature is wrong, or people are just plain ignoring what’s in front of their faces:  Low humidity + low mask use is now a recipe for disaster.  A public policy encouraging humidifier use (shooting for minimum 40% relative humidity indoors) might be as effective as a mask policy.  Particularly if Iowa is an example of the sort of mask policy that we can expect to see in the coming weeks.

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.