[quote switchname]@CrunchyCarrot
You mention asymptomatic people, but what about others who have had the virus mild-moderately, i.e. ill but nowhere near hospitalised (like me).
What does that tell you about longer-term immunity and immune response? I'd be grateful for your thoughts.
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Well let me say from the outset I'm certainly no expert on this. I've a biochemistry degree so am a scientist by training, but not a virologist/immunologist. During this pandemic I've tried to make sense of what's going on via a science-oriented perspective, particularly looking for research papers or discussions by scientists on YouTube.
My DP had Covid mildly, very mildly really. Just with a high fever for a few days, then he recovered. Fortunately no lung involvement. As I said up thread, I had Covid asymptomatically at the same time (only found out later via an antibody test, as DP had a positive response and I thought I should check myself). After that I've been very curious as to why some people are asymptomatic or shrug off the virus quickly, whilst others get very ill or even die. How can some of us get over a virus so fast when it's a novel virus?
What I've found out via reading is that the SARS-COV-2 virus has a 'trick' and that is that it's pretty good at evading our innate immune response, which is the first thing that kicks in when you get infected with anything. As a result, the virus can get a better head start so that one's immune system will then be playing catch up to get it under control and get an adaptive immune response going (the T cells) which happens around a week into infection. For those who become very ill, they have a weaker T cell response and cannot get the virus under control easily, or perhaps at all. For those who show a good T cell response, the virus gives a milder version of the disease and they recover. Of course there's a spectrum ranging from asymptomatic all the way through mild, moderate, severe and death. It's very much an individual thing.
However that still didn't explain to me how some folk are asymptomatic in the first place, or only very mildly. The answer could lie in past Coronavirus infections and T cell memory, apparently. There is some cross-reactivity between the Coronavirus family so this would give some of us T cell memory, potentially enough to fight off the virus very rapidly. This has been shown to happen in related flu strains. So perhaps we've had some Coronavirus infection in the past which is enough to arm our T memory cells with enough info to quickly mount an attack on the SARS-COV-2 virus. That's where my thoughts are, currently. I find the whole subject fascinating.
Pre-existing immunity to SARS-CoV-2: the knowns and unknowns
www.nature.com/articles/s41577-020-0389-z
There's also this seminar, came out in the last week:
T Cells: A New Hope for Lasting Protection against SARS-COV-2 (came out 5 days ago):