Seroprevalence only measures anti-body resistance, but SARS-CoV-2 is quite similar to common cold viruses and it appears many people have pre-existing immunity

Seroprevalence only measures anti-body resistance, but SARS-CoV-2 is quite similar to common cold viruses and it appears many people have pre-existing immunity to it for that reason. Or so goes the theory. The 20% antibody threshold seems to be fairly common across many countries however, at least outside non-China Asia/Pacific countries that were not badly affected at all. The body learns how to fight viruses and can do so quite quickly.