Coronaviruses aren’t all the same. That label really just refers to a general structure and says nothing about the antigens or behavior. For instance, HIV is a coronavirus. Are you saying if I get SARS-CoV-2, I’m now immune to HIV? Because I’m pretty sure I’m not.
The only other species to share the Sarbecovirus subgenus with SARS-CoV-2 is SARS-CoV (AKA 2003 SARS, about 9,000 people in the entire world infected). Sharing the Betacoronavirus genus are MERS-CoV (MERS (about 1,000 cases in the world) and HKU1 (under 100 cases in the world). Nothing else in the genus infects humans.
In other words, when we look at things that are at least somewhat similar to SARS-CoV-2, we’re looking at around 10,000 people out of 7,000,000,000 who would have had a previous infection with any chance at providing any immunity.
Did you read the article and the links?
They do not KNOW yet what MAY have triggered T cells that may protect 70% or more of the population from covid infection, But it is a theory of why about 20% of a population may contract the infection and 80% not, as on the Diamond Princess cruise ship. Which is why the virus infections decline in populations that reach 20% infection/exposure
It fits the models of peak and decline drawn from recent outbreaks. Which are the same for lockdown vs nonlockdown strategies
All of this is good news if time proves Farr, Leavitt et al correct
Not good news for vaccine investors