Though that’s about the common cold, not covid. She does mention covid in a comment:
For covid in particular the hypothesis was that it prevented transition between an annoying but harmless-to-most upper respiratory infection, to a very serious lower respiratory infection. I don’t know if that panned out for covid or if it transfers to other viruses, but it seems very plausible. “Nasal infection unaffected but progression to lungs inhibited” is an extremely specific prediction that should be fairly easy to measure but I couldn’t find anything on it in a few minutes on google scholar, which I find very disappointing.
Though that’s about the common cold, not covid. She does mention covid in a comment:
It’s thought that it applies to coronaviruses in general.