I'm curious - how are you certain that it's Coryza? Is there a strong, fetid odor to the gunk in the nostrils? Which antibiotic are you using?
The way I understand it, generally you don't want to vaccinate carriers unless you're trying to illicit an immune response to try to keep down vertical transmission into eggs (and then I've read only about that in infectius synovitis - haven't researched it otherwise).
There seems to be an indication that using an initial vaccination at 10 or so weeks, and another approximately a month later can decrease incidences of coryza in the flock. That according to one vaccine manufacturer.
But birds are carriers. So you will have to vaccinate and allow the booster to take hold before introducing them to your existing flock to really take advantage of the vaccine's mechanism.
Does that help?