Nasal sprays have certain advantages but also still require some breakthroughs in development to provide an end game. Potentially they allow convenient use, the ability to potentially block the virus from even getting a grip in the first place (which has huge advantages over leaving it to a trained immune system to fight it) and the ability to be used much more precisely to fight an outbreak - if you've got something which a couple of shots up the nose before and/or after you are spending time in environments ripe for transmission, which provides a high barrier to the virus, that can stop outbreaks dead in their tracks.