[quote amicissimma]**@RobinHobb* and @BogRollBOGOF*, this is the thing.
We keep hearing about how someone had Covid, tested negative, then tested positive again, so 'had it twice, so there's no immunity'. But it seems to me that it means the opposite - that having had it once the person has developed antibodies, or T cells, or some way that their immune system is primed, so when they encounter Covid again, as soon as it enters the nose/throat, the immune system deals with the virus and they end up with a whole load of de-activated viral particles which are picked up on a PCR test. The 'repeat infections' tend to be picked up on routine testing, suggesting that the person hasn't had symptoms again.
We even hear that the PCR picks up viral particles of a different strain, which is taken to show that there is no cross immunity. But I can't see that. It seems to me that unless the person is really unwell again, which happens, but is vanishingly rare, a PCR test picking up Covid again shows that there is immunity, even to a different Covid strain.
And you might expect, if your immune system swung into action on encountering any pathogen that it had met before, that you might feel slightly 'off colour' while it did its work. Or you might not notice. I've had times when I thought I was getting a cold but it never materialised, presumably because my immune system did its job. Was I 'having' that cold? I'd say not.
As for spreading, I suppose there might be a very short period - minutes? hours? while there was live virus while the immune system was dealing with it, but it's likely that for some or most of that time the affected person was still in the place where they re-encountered it, so others would catch it from the original source, rather than people actively neutralising Covid being a serious spreading concern.
Anyway, I'm not an immunologist, but some of the hysterical claims seem to defy what biological knowledge I do have, combined with common sense.[/quote]
"as soon as it enters the nose/throat, the immune system deals with the virus and they end up with a whole load of de-activated viral particles which are picked up on a PCR test. The 'repeat infections' tend to be picked up on routine testing, suggesting that the person hasn't had symptoms again"
I don't think it works this way. What the PCR test picks up is a certain portion of the viral DNA. So if you have an infection with Covid (for the first time), your immune system recognizes there is an antigen, there is something called an antigen presenting cell, and series of steps, that leads you to produce B cells/antibodies that are tailored to attack the antigen (Covid). During this period the viral DNA works to make you sick, as the DNA replicates in the human host cells. The PCR tests pick up a certain portion of this DNA.
On the second time around you are exposed to the virus, the antibodies already exist and the virus does not replicate (and there is no viral DNA), and the PCR test cannot then pick this up. So you would test as negative. So basically, the virus would have to be alive and replicating (ie producing DNA) to test positive, and that's when you are infected.
In spite of this, PCR test etc, I am completely in agreement with the fact that we have epidemic of hysteria. I can't stand the hypochondria :-)