I'm taking a short vacation from physics this week to talk about long covid, which is a topic we'll be hearing a lot about in the next few decades.
Everything you know about polio is "long polio". Everything you know about AIDS is "long HIV". Shingles? Long chickenpox. Multiple sclerosis? Long Epstein-Barr.
"Post-viral syndrome" is a catch-all term for the bad things that happen after the acute phase of a viral infection.
Because it is difficult to define and even more difficult to treat, it has been a political football for decades. Our health care systems do very well with both acute and actionable conditions. Post-viral syndromes tend to be neither.
They are also ripe being co-opted by kooks: an ill-defined suite of symptoms that may be physical, mental, psychological, or emotional that allows people to loudly proclaim they are being let down by the medical establishment is just the sort of thing your average conspiracy prone nut-job would delight in having, doubly so if they can wangle a disability pension out of it.
And kooks exist.
So does post-viral syndrome, which is a real, serious, difficult to study, very difficult to treat set of conditions. Like cancer, it is not a single disease but a collection of completely unrelated diseases that have a common generic origin. In the case of cancers, that common origin is "uncontrolled cell division". In the case of post-viral syndrome it is "physiological response to past insult."
That response can take many forms. In many cases it is almost certainly primarily driven by the immune system: many post-viral disorders are auto-immune disorders. In other cases it is due to the virus not being cleared out of the body, but finding a way to silently screw up some organ system or another. HIV is particularly bad for this: it sequesters itself in CD4 lymphocytes, which are part of the immune system itself. In other cases there is damage to specific organelles, like the mitochondria.
There is some evidence that mitochondrial damage is implicated in long covid but it cannot be emphasized enough that we are still very much in the early days of this process of discovery.
Overly-rapid narrowing down and focusing in on a single hypothesis is almost always a mistake, but it takes great discipline to avoid getting caught in the cycle of confirmation bias that leads to this. We get an idea, and confirmation bias nudges us toward evidence that supports it. We find such evidence, always because there is no idea for which at least some evidence does not exist. We use that evidence to unduly boost the plausibility of our favoured idea, and continue to repeat the process.
Tells that this kind of thing is going on are statements or feelings like, "It all fits!" and "It's what I thought all along!" and "It all makes perfect sense!"
Any of those are very, very strong signs of an individual who has thrown knowledge to the winds and is completely unhinged from reality, because in reality, nothing ever fits perfectly, what we thought all along is never, ever correct, and nothing makes perfect sense. The only way for things to make perfect sense is to deliberately ignore the things that don't.
In the case of long covid, there will be at least three groups of motivated reasoners whose loud, stupid, voices will dominate the debate, at least in the early phases:
1) Denialists: these will be bureaucrats, scientists, and clinicians who don't want to deal with the messy reality, so they will say everyone who has long covid is a kook (which exist). They will point out that the range of symptoms is so broad as to catch anyone with so much as a hangnail after they've had covid, and pretend it's all a big nothing burger. The closer to government a person is, the more likely they will be in the denialist camp, because long covid is going to cost a lot, and governments would prefer it didn't exist.
2) Maximizers: these will be people suffering from long covid, as well as scientists and clinicians who see it as an opportunity to study something challenging and new. They will say "80% of people have long covid after infection" by maximally expanding the definition, and they will then argue about it as if everyone who meets their expanded definition has the most serious symptoms, which is a kind of motte and baily argument, much beloved of social problem maximizers everywhere: redefine a problem so broadly that no one would care if everyone had the most tenuous version of it, then treat it as if everyone who has the most tenuous version actually has the most serious version. It's a form of purely dishonest fact mangling that comes from insisting there is only One Real Category, rather than a bunch of epistemically useful sub-categories with quite different characteristics.
3) Woo-ists: they will muddy the picture by maximizing and specializing in specific "cures" for particular symptoms. The symptoms they focus on are the ones that are the most difficult to define or measure objectively. Any long-covid symptom that a major woo-ist claims to be able to treat should be categorized into a different syndrome. Such symptoms may still be very important, but they should not be allowed to mix with the objectively measureable symptoms that woo-ists can't easily manipulate.
4) Scientists: they are the poor souls whose work will be reinterpreted by the above groups in any way that can be used to the group's advantage.
You can already see some of this starting to happen, particularly with the manufacturing of attention-grabbing numbers.
What we should be doing to communicate about this more clearly is to focus on single symptoms: fatigue, for example, which has fairly good objective measures.
When we are studying something new, there should always be a phase of exploratory investigation whose goal is to find definitions that allow us to generate reproducible effects. In this exploratory phase, objective measures should be given a very strong preference as the only way to avoid the influence of motivated reasoning.
The influence of motivated reasoning is so large, and so well-known, and so well-documented, that there is really no plausible motive for not giving preference to objective measures in this critical exploratory phase except to allow motivated reasoning more scope for action. This translates into "more undue political influence on the part of the investigator", which never leads to new knowledge.
Fortunately, we are in an era where there are a variety of objective measures of fatigue under test, and no doubt there will be more to come. So at least no one anywhere can ever again say, "Well, we can't even measure fatigue objectively so how do we do anything about it." Although some will, and like people who say "We knew it all along!" the fact they are saying it will mark them as insincere, highly motivated, individuals who have no interest in contributing anything useful to the discussion.
When a topic is complex and important and new there will be a lot of loud voices trying to gain influence and status by lying about it. Having heuristics to identify those people is important to tuning them out.
So is being aware of the biases of the people trying to be honest. Given what we know so far, I'm betting that no more than ten percent of covid cases result in significant long covid—that’s the current low end number based on studies using tight rather than expansive definitions—but that we'll routinely hear 50-80% being bandied about despite the fact that we will all know ten people who had covid and no more than one who has significant long covid.
That disconnect will help discredit the real numbers, which are still very bad. There is every indication that post-viral syndrome in covid will be a significant factor in human health in the next several decades.
We owe it to ourselves and each other to be as clear and objective as possible when defining it, to not inflate or deflate numbers based on the political or economic impact we think they might have, and to split the single "long covid" category into meaningful sub-categories in the cases where the data warrant it.