https://judithcurry.com/2020/07/27/why-herd-immunity-to-covid-19-is-reached-much-earlier-than-thought-update/#more-26449
A key reason for variability in susceptibility to COVID-19 given exposure to the SARS-CoV-2 virus causing is that the immune systems of a substantial proportion (35% to 80%) of unexposed individuals have T-cells, circulating antibodies or other components that are cross-reactive to SARS-CoV-2 and can be expected to provide substantial resistance to it.[6] [7] [8] [9] Such components likely arise from past exposure to common cold or other coronaviruses, or to influenza.[10] Not being specific to SARS-CoV-2, and typically not being antibodies, such immune system components are not normally detected in seroprevalence or other tests for immunity to SARS-CoV-2.
I will end with a follow up to my June 28th article focusing on Sweden. In it, I concluded that it was likely the HIT had been surpassed in the three largest Swedish regions, and in the country as a whole, by the end of April notwithstanding that COVID-19-specific antibodies had only been detected in 6.3% of the population.[11]
Good stuff, CD. While I consider her website to be potentially in the area of "biased", I appreciate that she actually cites sources directly, and so I clicked through to sources 6-10 linked.
I'm not an epidemiologist, so some of it was over my head, but it definitely suggests that there is some level of protection for individuals who have T-cells that are cross-reactive to this. Basically that some of the T-cell memory from other coronavirus spike proteins make it more likely that they will recognize the structure of SARS-nCOV-2 and have a better outcome fighting it.
Highly interesting, and may explain why we have such divergent outcomes even beyond just age/health, including so many asymptomatic carriers.
I hesitate to agree that this will stop the spread, necessarily, though, as we know asymptomatic spread is still possible, and having these T-cells doesn't mean you're immune from contracting the virus, only that you may have a much higher likelihood of good outcome. So per Badge's conjecture that 40-50% of the country "has had it", I think what this might be showing is that roughly half the country may have a level of immunity that will protect them from the worst outcomes of this thing...
Thanks for posting. Appreciate the evidence.