Brit, this is not what you asked (when did that ever stop an EF discussion

) but should the Vetriderm turn out not to do the trick, this new research by the Tierspital and Uni Zürich might be of interest to you:
http://www.usz.ch/news/Mitteilungen/...rallergie.aspx
Not planned to be introduced until 2022 - but something to discuss with your vet, and of course if you were to consider this route you'd want to discuss it at length (efficacy, safety, etc.) with the Tierspital researchers, as this is a totally new concept. You'd also want to discuss this with your allergist.
Anyway, just something I found on my way to looking up something else, so I thought I'd toss it out there. Due diligence required, of course.