InVitroInVivo, Redux

Kady M.
9 min readMay 29, 2021

(Originally wrote this one on March 9. New information has come to light since, making me feel really good about the original article. New discussion in the section below marked UPDATE.)

There are four groups of people who read that title:

  1. You didn’t take life science courses, and you think that this might be a nice article about a new Italian restaurant.
  2. You did take life science courses, forgot what that meant, and I just gave you an unpleasant flashback to something you would have rather forgotten.
  3. You did take life science courses, work in specific areas of life science related to these terms, and therefore know EXACTLY what they means, or
  4. You’re a high school Latin nerd, and got all excited to see Latin. :-)

Anyway. :-)

In Vitro refers to the testing of a process in a controlled, laboratory environment. In Vivo, on the other hand, refers to the “testing” (so to speak) of that same process in a real world environment, exposed to other variables that might be present in said environment.

The difference between the two is well known to those heroes of science who create vaccines. It is not uncommon for a vaccine to utterly destroy a pathogen in a test tube in vitro, but when animal or human in vivo testing starts, find that the vaccine is utterly useless. For lots of reasons.

Well, the same sort of discrepancy has popped up with, of all things, mask wearing.

One of the unpleasant byproducts of the COVID pandemic has been to produce a subclass of moral scolds who will not only mercilessly berate mask-critics on social media, but also do so in real life, where their utter indignation at individuals choosing to bareface sometimes turns to physical confrontation.

For example:

The unfortunate part of all this rancor is that mask-wearing appears very much to be one of those things affected by “InVitro vs InVivo”.

How? Well, scientific study after study has proven that mask wearing reduces both the amount of viral load expelled by an infected individual and inhaled by a healthy one, thus lowering risk for contagion rather significantly. Good news.

However, these studies have been done either under lab conditions or in semi-controlled environments so data can be gathered. In other words, “In Vitro.”

Unfortunately for those studies, however, when we look at mask-wearing in broad populations over time, In Vivo, well, the advantages are….somewhat hard to find.

Now, I’m not suggesting we dispense with masks. I tend to believe that in certain environments they probably do a lot of good; it’s just that as a population, we spend more time outside our homes in environments which they don’t do much good. The 60-foot-ceiling inside of Home Depot or Wal-Mart, along with its industrial strength air conditioning units, probably isn’t tremendously different, in terms of risk of contagion, with a stroll outside in the park, as long as reasonable distancing is observed. Lots of space with clean air being piped in and bad air being filtered out.

But for mercy’s sake, stop throwing rhetorical bombs (or worse, fisticuffs) at people not as dedicated to their masks as you think they should be. It gets us nowhere, divides us even more than we are otherwise, and is generally counterproductive as we move through what we hope are the latter stages of the pandemic. In Vivo, we find that the difference between masking and not is simply not as huge as those In Vitro studies originally indicated.

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Been reading some recent information that reinforces why masks, in vivo, aren’t the defensive armor that many thought. Let’s start with mask fit.

FIRST: To start, here’s some conclusions from a Chinese paper published in JAMA in March. Some operative quotes:

First, this study reported that the airtightness of face masks in community populations was suboptimal, which may be a reason why many countries have reported a great number of COVID-19 cases despite face mask use, including among medical staff and passengers on public transit.6,11–13

And also this:

The researchers, from the University of Cambridge, carried out a series of different fit tests, and found that when a high-performance mask — such as an N95, KN95 or FFP2 mask — is not properly fitted, it performs no better than a cloth mask.

To bring this down to simple terms, everyone has had the experience, if you wear glasses, of glass fogging when you breathe. Unsurprisingly, if you’re infected, that “leak” contains virus. And if each time you exhale, you’re expelling virus into the environment, the problem is obvious.

What studies are showing is that most mask wearers do not properly fit their masks (which would require, in the view of researchers, a layer of adhesive tape along the top edge of the mask under the eyes) and because of that poor fit, mask wearing is far less effective (here we go again) in vivo than it is in vitro.

Now, the quick witted among you will say “Yes, but if they’re no good, why do doctors and nurses wear them in surgery?”

Well, because masks are far more effective in the controlled environment of the operating room, and they are being worn by people who know how to wear them effectively. So, yes, you’re right — — even there they are not perfect, but they are far more effective there than for somebody who throws one on so they can pick up some donuts at Wal Mart.

SECOND: Single Use

The aforementioned paper went on to state:

It is common that face masks are worn beyond their expiration time (typically 4 hours),14–17 which could be one of the major risks. Improper face mask use is a challenge to pandemic control in public places.3,18–20

The ubiquitous blue mask, which is more efficacious than a bandana or other cloth covering (neither of which were found to be particularly protective in lab tests, is designed for single use:

Why single use? Well, if you’re breathing through the mask (and not around it, which doesn’t protect you at all) in an environment where airborne virus exists, the virus (in a perfect world) sits in the fabric on the outside of the mask. If you remove the mask and re-use it, not only are you touching the mask (increasing the risk you transfer the virus to yourself on your hands) but the virus has a greater chance of working through the fabric on next use, and into your mouth or nose.

It’s interesting to me that the government, for all their advocacy about mask-wearing, hasn’t emphasized this point more; I suspect it’s because single-use masking becomes expensive, and they realized that adding a financial arrow to the quiver of the anti-maskers could lead the public to rejecting masking in much larger numbers. We’ll have to wait for Dr. Fauci’s memoirs on that question, unfortunately.

That said, I would love to see data on how many of the masking zealots were disposing of their masks after each use. If they weren’t, they were defeating their own purpose, to some extent.

(I’ll add here that the more expensive but also more protective KN-95’s are also designed for single use, but can be cleaned, whereas the blue mask above breaks down on an effective cleaning. But how many KN-95 users were taking the time to clean their masks?)

THIRD. The debate about aerosol vs droplet transmission continues, with large implications to the efficacy of masks.

Masks are highly useful against droplet transmission, which is how virus spreads when people are coughing, sneezing, singing, or (probably) giving long political speeches. That makes sense; droplets are big.

HOWEVER, droplets quickly fall to the ground (gravity, after all). So, if you maintain social distance from the cougher/sneezer/singer/demogogue, your risk of catching disease from said person is already low. And….you don’t need a mask to protect you from what’s not there. :-)

But, there’s also aerosol transmission, which is where the virus is traveling in the air on its own for longer periods of time, and virus being as small as it is……masks don’t protect you from that.

The CDC is still studying this problem. But suffice to say that the efficacy of mask-wearing is affected by the % of total expelled viral load present in droplets vs aerosols.

— — — — — — — — — — — — — — — — — — — — — — — — —

So, let’s sum up.

This article, both the original and the update, point out some of the reasons why masks, although affording some cursory amount of protection from viral transmission, are certainly not any sort of invulnerability shield against catching a disease.

And at this point in the pandemic, with USA first-vaccine reaching close to 50% of the population……well, to be honest with you, I’m done with masks. The data and studies cited above lead me to conclude that for vaccinated me, all they are is an annoyance, providing me no additional protection in the least, and certainly not protecting anyone else FROM me. And since I’m not political or tribal on this issue, I really don’t care what anyone else thinks of me. (I am totally repelled by what I’ve seen from certain people on social media, that they know that masks aren’t very useful for them, but they wear them anyway so people won’t think they’re Trumpers. I would highly advise such people not to give others so much control over their own behavior.)

But the same is close to being true for everyone. I haven’t completely fleshed out my thinking on this, but it occurs to me that although there’s such a thing as the well cited “herd immunity” (70% of everyone is immune) but also something that perhaps should be called “effective herd immunity” where the chances of an un-vaccinated individual, who is still cognizant of social distance, encountering enough virus to become ill is so low it becomes an afterthought. Time will tell.

In closing, one thought about “science”. I am normally a nonviolent person, but I am starting to become homicidal when I hear non-scientists say “I follow the science.”

“Science” is not imparted by politicians or government agencies. They have, and always have had, a vested interest in making certain types of problems (where they want the public to behave in a certain manner) sound worse than they really are. Fear drives behavior. Always has.

“Science”, OTOH, comes from scientific studies, experiments, the papers the scientists write, the small number of journalists capable of reading said papers and honestly explaining them to you (

, for one, who recently wrote an article which approached by idea of “effective herd immunity” from a different angle, and without calling it that), and from …. STATISTICS.

You see, statistics is not only a science, but it is the science that science often depends on. When we’re analyzing the effectiveness of masks and other kinds of mitigations, the statistics IS the science. What % of viral load does a fully fitted mask protect you from? What is the % if the fit is poor? What % of total virus is droplet vs aerosol? What % passes through various mask material?

It’s all stats, folks. So when somebody says “I follow the science” and then they try to explain away why Texans didn’t die after the mask mandate was removed….

…they aren’t following the science; the science is clearly indicating that the pro-mask politicians and government bureaucrats are the ones “not following the science”, albeit understandably, for public health reasons.

Enough said.



Kady M.

Free markets/free minds. Question all narratives. If you think one political party is perfect and the other party is evil, the problem with our politics is you.