What about whether or not you can "catch it again" once your immune system has beaten one version?
I've read in the press that corona virus might be biphasic, which is a big problem for an air-borne transmissable disease. In the jet age, quarantining potentially thousands or millions of passengers becomes expensive and disruptive when there's a week between phases.
Lyme disease is like that. First you get a bullseye rash and flu-like symtoms, it goes away, then later your organs are attacked.
https://en.wikipedia.org/wiki/Biphasic_disease
That's different than a chronic disease, where you never recover.
Shouldn’t the first phase act as a sort of vaccine?
This is purely based on other comments I've read, I personally know nothing about viruses.
Technically not true - coronaviruses cause 15-30% of common colds. The most common cause of the common cold is rhinovirus (30-80%); coronavirus is next, followed by influenza (10-15%), adenovirus, and then other viruses like RSV. The rest of your comment is fairly likely IMHO, though.
I’d think you’d never clear it to begin with if that was the case.
> "After exposure to one strain of virus, these memory cells are then better able to recognise variants of the virus if they encounter them in the future. The immune system learns to protect against a whole group of related viruses, not just the one it experienced."
Say the virus mutates so that only 50% of its features are recognizable.
You'd think that the fact that your cells can recognize this is good, and it is to some extent, but, it also prevents new cells from learning about the virus(in efforts to prevent autoimmunity in analogous scenarios with non malicious objects; our immune system has to walk the fine line between being too permissive and allowing infections, and being too restrictive and murdering its own host through nasty autoimmune diseases).
So, it mounts a 50% response, which is often good enough, and more than makes up for the more limited response with speed.
But what happens when the % recognizable drops to like 3%? Some percentage of cells will recognize the 3%, and be able to mount a weak response, but more critically, block other cells from developing new responses. This limited response will slow down a proper response and itself will be likely ineffective.
Its known as "original antigenic sin", if you want to read more.
It's also unknown whether it's possible to develop immunity to COVID-19 at all, with reports of reinfection in both China and Japan.