Believe it or not many people have a mucosal resistance and the virus never has a chance to replicate. Stopped at the front door. That immunity varies by individual. See UK Challenge Study (https://doi.org/10.1038/s41591-022-01780-9).

I try to avoid respiratory infections via mouth/nose sanitation like was done eons ago. I use a dilute Betadine solution other do fine with simple salt. So very odd our masters of public health can't be bothered to do a PSA. Doctors, some of them, say it works.