That's the way I'd interpret, too, Jess.
From a racing/training perspective, I used to vaccinate 3 monthly, the immunity conferred is very short-lived, so my veterinary advice indicated.
But I have to admit that in recent years, I haven't been as religious, every horse will have antibodies to EHV [ unlike back in the seventies, when it appeared in a largely naive population - again, as I was told ]. It seems that there is little concern from a practical point of view about EHV infections in racing horses. If there is, I haven't been informed.
WRT the strain affecting breeders, I have little experience with that - viruses are of course a very different animal from the bacterial infections, i.e. strangles - but it astounds me that many trainers, when faced with a possible case of that, close ranks, swear everyone to secrecy and keep it all quiet. So, so stupid - and thoughtless, when transport operators and the point of origin of the affected horse should be notified so they can take appropriate measures themselves.