Those probably aren't good diagnostic criteria for any specific virus
I think I burbled on about this elsewhere, but the essential problem here is one of belief. Even if someone catches Covid-19 - even if they end up being treated for it - they are, at the psychological level, still dealing with something they can't see, touch, smell, or sense in any way: so it's all about whether we
believe it represents a risk. And the problem with belief is that it's very flexible - there's no "risk-o-meter" sitting along the bottom of our eyeline to tell us how much risk we're at.
So, on that basis, someone is able to believe in the risk enough to put on a facemask, go into work, do their job taking all necessary precautions, etc. But, through every moment that they're doing that, the belief that they are at risk becomes more and more difficult to sustain - "I've been working in my job for 3 weeks, and haven't caught it, so it is less of a threat". Rinse and repeat. Slowly, without that belief being topped up with facts - facts that, likewise, we are able to
believe - it becomes weaker, and the steps we take to protect ourselves become less important. Or, as
LynnDoyleCooper just pointed out, we add a belief - "I've already had it, so I'm safe"
To some extent, we'll all be doing this - to reference Kahnemann again, it's all about System 1 thinking ("fast" thinking). The counter to it is to invoke our System 2 thinking - and a lot of the discussions in a forum like this, where people like
elbows are producing facts, stats, figures, people like
LynnDoyleCooper are providing a combination of front-line reports and medical knowledge, are essentially doing the System 2 thing. But there's a couple of problems with that: first of all, lots of people don't really
do System 2 thinking: it's often the kind of thing that emerges from even quite a basic scientific training, where, along with finding out what happens when you do some basic chemical experiment, you're also learning that "what I intuit" doesn't necessarily follow in objective reality. So people without that training will find it harder to make judgements based on facts they can't actually see for themseves. And the other thing is that System 2 thinking is hard work - walking into a Tesco where hardly anyone is wearing a mask, the old System 1 kicks in and says "look, it can't be risky, because those people don't think it is, also I don't want to stand out or look stupid", and it can take a conscious effort to go into System 2 and say "butbutbut, the numbers say that people ARE getting infected, people ARE dying" at a time when it feels less immediate or relevant than putting ourselves to the inconvenience of masking up.
I'm not even pontificating here - what I described in the passage above was
exactly the thought process I noticed myself going through as I walked towards my local Tesco. OK, I did mask up (I went to another personal System 1 belief of "fuck you, I know better than you, and I'm doing the Right Thing, dammit"
).
As with any kind of large-scale threat, the human factor - what we believe, and what we do with those beliefs - is a massively significant factor, and one that I think is often discounted or ignored.