Search for carrageenan nasal sprays
I was doubtful at first but that sh^t really works wonder, even my cousin who's a weak thing that used to collect pretty much every seasonal virus and tried pretty much every other thing on the market (that usually don't have virucidal properties but are merely decongestants) says he gets ill much less
Also supported by some placebo-controlled trials e.g. https://pmc.ncbi.nlm.nih.gov/articles/PMC8204093/
Bonus it's completely harmless to you; it's basically the same thing you put e.g. in custard to make it more dense lol