Fair point. I still think pre-existing sterilizing immunity is unlikely, since (to my non-biologist's understanding) antibodies tend to be specific, and T cell

Fair point. I still think pre-existing sterilizing immunity is unlikely, since (to my non-biologist's understanding) antibodies tend to be specific, and T cell immunity is broader but not usually sterilizing. The existence of those unlucky groups isn't conclusive evidence in itself, though, especially if pre-existing immunity is distributed non-uniformly (which it probably is, if there's some genetic basis, or if different strains of common cold coronavirus swept through different regions last year and primed people's T cells differently). Of course non-sterilizing immunity could still be incredibly valuable. They're speculating that the current vaccine candidates may not cause sterilizing immunity[1], but immunity that turns a fatal illness into a bad cold (or a bad cold into a couple of sniffles) is great, whether naturally pre-existing or from a vaccine. 1. https://www.statnews.com/2020/05/22/the-world-needs-covid-19-vaccines-it-may-also-be-overestimating-their-power/ https://www.statnews.com/2020/05/22/the-world-needs-covid-19...