usually the intranasal Modified Live Vaccine are pretty good - usually IBR combined with PI-3
the main advantages is you some sort of protection with 3-4 days after inoculation; questionable interferon activation tho
it gives a quick boost, but usually immunity is not as long as injected MLV
i like to use it in show calves (7-9 month old)... give then the typical injectable MLV at/near/before weaning and then about 2 days before heading to a show give them the intranasal and seems to work pretty good
some problems people have had is giving an injectable MLV too soon after giving the intranasal; the immunity from the intranasal blocks the effects of MLV and then end up getting respiratory disease further down the road
as long as some of the product is getting up in the nose there will be some immunity -- head restraint and speed of delivery are key to proper application
JWW