Do you have any links?
I find it hard to believe that bicarb has absolutely anything to do with preventing COVID, except maybe because it blocks your nose?
the bicarb & saline are purely for comfort. The one time I left them out, I was reminded why people shy away from putting water up their noses: it burns.
Searching Google scholar only shows one paper with about 60 people reviewed and an improvement of 30% from the control group not getting COVID, to 40% didn't get COVID if they washed their nose. Not exactly great numbers when you have so few people.
I don't see anything serious about your theory.
https://www.uclahealth.org/news/nasal-irrigation-may-help-wo...
https://www.sciencedaily.com/releases/2022/09/220913110403.h...
sample size of 79
Aside from the formal research, there is clinical support for it: just ask your doctor. Most likely he or she will say, "Sure, go ahead. A lot of my patients do it." That's what mine said.
And finally, I've found on previous social network discussions (including on HN) that the practice is fairly widespread.
And there are peer-reviewed studies about its efficacy.
On the other hand, I don't have kids & wasn't in crowds very much, so there's that.