[bsder]

It would be nice to have a dosage that lasts a couple of days for when you're flying or attending a conference.

That way, your immune system wouldn't be on continuous high alert, but you could give it an "Oy, wake up. Incoming pathogens." blast.

[jalapenos]

This. I don't think humans have evolved a brain - immune system pathway to prime the macrophage pump after you book a Ryanair.