And you can buy it in shops!
https://www.boots.com/nasaleze-travel-barrier-spray-800mg-10279758

I *assume* protection only lasts a day or two, and you have to keep using it to keep the protection up. Whereas a nasal vaccine would give long-lasting protection.

But I can't find any details on how long it lasts, which I'd love to see.

But still, that's amazing, and I want to know why I hadn't heard of it before!