The Covid-19 pandemic is serious, scary, real, and kills. And there is a fair amount we don’t know about it.

There I said it. You don’t have to worry about me thinking Covid-19 isn’t serious. That happens to me a lot. Someone says “OMG, the COVID-19 is just like a grizzly bear eating your face off!” and I point out that a virus and a face-eating grizzly bear present distinctly different problems. Then the person gets all pissy and mad because I did not share their specific horror. Generally, I prefer it if people do not shove their fears in my face at the expense of reason. We have real fears, we don’t need to add on the ones that are bogus, unsupported, panicked, or untethered from reality.

You might say, jeezh, Greg, what harm does it do if people don’t understand every little thing about COVID-19 and, in their conceptualizing this disease, stray away from actual science and reality and stuff? Most of the time it probably does’t matter. But people make decisions on the basis of what they think they know. If you think the SARS-CoV2 virus doesn’t really live on surfaces, you won’t be careful about door knobs and push plates in heavily used public places, and you may thus contribute to the spread of this disease. If you think COVID-19 can be spread by eating food from a can, you might waste your energy, my energy, everybody’s energy, by campaigning against canned food. And so on.

So what kinds of things are people getting wrong? Here’s a sampling.

COVID-19 is caused by a virus. Most life lessons about pathogens are not transferable across types of pathogens. A coronavirus can’t be compared usefully to malaria or sleeping sickness because those are single celled eukaryotes. COVID-19 can’t be compared to bacterial infections. All these different kinds of pathogens have different effects, do different things, act in different ways, and need to be dealt with using specific actions (or avoiding specific actions).

COVID-19 is caused by a particular type of virus. There are many kinds of viruses, and the different kinds have distinctly different biologies. Comparing the behavior of SARS-CoV2, the virus that causes COVID-19, to the influenza virus, is like comparing the behavior of eels to eagles. How they reproduce inside a cell, how they avoid a body’s immune response, how much they mutate, and how a vaccine might work for each type of virus, are really very different, in fact, astonishingly different. Comparisons are not helpful at all.

Immunity is a tricky concept to understand. I wrote about it here. I think immunity (to a pathogen) is often viewed as an absolute, and as a somewhat magical thing. If I’m immune to a particular pathogen, that pathogen can not infect me, right? If I’m walking down the street, and a pathogen is coming the other way and I’m immune to it, it crosses the street to not get anywhere near me, right?

No. If I’m what we call “immune” to a pathogen, that means that the pathogen still goes inside me. It starts to do whatever that pathogen normally does in a human body. It is, in fact, infecting me. Then, because I’m “immune” a particular part of my immune system quickly responds to that pathogen’s presence, because I’ve acquired an immunity to it either by prior infection or by vaccination. Other parts of my immune system also work against a pathogen whether I was previously vaccinated or exposed or not.

The acquired immunity that comes with vaccination or prior exposure causes my body to respond more quickly. The best kind of immunity is where my body responds well within the time period where the pathogen hasn’t made me sick yet, attacks the pathogen, and kicks the crap out of it before it can do anything. I don’t get “sick” from the pathogen not because it did not infect me — it did infect me — but because the illness that pathogen typically causes never got of the ground. The natural biological course of the pathogen did not advance sufficiently to either make me feel bad or to be passed on to another person. Or, in a less ideal immunity, common with many pathogens, I do actually get somewhat sick, and maybe I can even pass the disease on, but acquired immunity makes me much less sick and much less contagious.

And as noted, a person who is “not immune” is typically a little immune anyway. That is because the immune system has several parts that try to stop a pathogen, and because the above mentioned acquired immunity is still an immunity before it is trained up in your body. It just takes longer.

The difference between a typical “non-immune” person and a typical “immune” person, as the term is usually applied, is this and only this: For the immune person, the adaptive immune system (only one part of the immune system) acts faster because it is trained by prior infection or a vaccine (which simulates a prior infection) so the body is prepared.

Indeed, a normal immune response to a pathogen is often to get sick and seem not very immune at all. Little kids get colds all the time, and they can last a long time. It seems like from a certain young age until a few years later, still at a young age, a kid is sick all the time. Adults go around bragging about how they haven’t lost a day of work in 20 years. (Not all adults, but some.) This is largely because kids don’t have a very strong immunity to the handful of different viruses that give us regular colds. But over time, a human will typically develop a stronger and stronger immunity. All these humans are immune to those viruses to some degree, just not perfectly and totally immune.

With COVID-19, we hear stories of “reinfection” and this has led many people to believe that humans do not develop an immunity. The numbers of possible re-infections is very very small compared to the number of people infected, and it is highly likely that those instances are bad reports, or individuals who never really got rid of the disease to begin with. Of the remaining, much smaller number of individuals, re-infections may have happened because that person’s immune system just didn’t produce a strong immunity in that person. A very small number of possible re-infections is expected for any disease and isn’t alarming.

Usually, an exposure to a pathogen that we can develop an immunity to results in an immunity that lasts for a while. Usually, years.Sometimes enough years that it seems like a life long immunity, or close to it. In other cases, you get a modest immunity that gets better with more exposure. Remember, SARS-CoV2 is a particular virus, and should not be compared willy nilly to other viruses. HIV gets around the human immune system, but it is a very different virus. Not a valid comparison at all.

Sometimes our immunity does not help us much with a later infection, or so it seems. You get a Yellow Fever shot and later they tell you you need another one. Or, the flu shot from last year isn’t helpful this year. This might be a linguistic matter. We call the pathogen by a certain name, but underlying that name is a wide range of different species or strains of that pathogen. We use the word “flu” for “influenza” but there are many different major types of influenza. If influenza was a “canid” then there would be foxes, wolves, coyotes, and domestic dogs. All in the same family but not really the same.

Alternatively, later infection could be the result of a particular strain mutating enough to side step our immunity, somewhat. Or, it could be that our immunity wore off.

A common misconception about mutations is that they make a pathogen worse. Well, they can, but they usually don’t. We hear “COVID has had 29 mutations! Aieeeee!!!” I assure you that SARS-CoV2 has had many many more mutations than that. If you get COVID-19, the SARS-CoV2 inside you probably mutates hundreds or thousands of times as it replicates using your cellular machinery, as viruses do. But, the vast majority of mutations cause a viral strain to become broken, or to not change at all. A small number may make the virus a little better at what it does, or a little less good at what it does. From our point of view as the host of the virus, a small number of mutations might make it harder to pass it on, or easier to pass it on, or liable to make a person a little more sick or a little less sick. That any one of these mutations occurs in your body does not mean that that mutation will now be part of the general population of SARS-CoV2 viruses. The vast majority of mutations that both happen in an infected individual and that do not produce a dead-end variant will not be passed on to the next person. You will just sneeze them out and they will be killed by ultraviolet light, hand sanitizer, or the main thing that kills most individual virus particles: Time.

We hear a lot now about rare and scary things. Twenty-three year olds dropping dead of a stroke, or other odd blood clotting things, and so on. Those may be real or they may not be real. If tens of millions of people get a disease, there will be situations where a cluster of individuals were going to also have some other thing happen to them medically, and they happen to have this thing occur while they have COVID-19. Coincidence. Or, a disease like this might really have some other effect that is very rare, but that thing is, well, very rare. After the discovery of some possible odd effects on blood clotting, people started to say things like “it kills young people in this strange way and we didn’t know it until now! Aieeeee!!!!” but at the same time, the death-over-age statistics did not change. We did not find 300,000 dead 23 year olds. The strange new thing remained rare, and enigmatic. Important, interesting, something we must find out about. But still very rare.

I’ll end here with a dirty little secret of the immune system: Of all the different biological systems that make up the typical animal (including humans) it is with the immune system that the gap between all that can be known and what we confidently know is largest and deepest. We know a lot, but we also don’t know a lot. And, it is so damn complicated that it is impossible to expect the average non-expert to not make the sorts of mistakes mentioned above. I can add this: I’m heavily revising what I cover in my course on the immune system, to help future generations of pandemic victims have an easier time parsing what is happening around them. Assuming I can get back into a classroom with them!