Not sure you'll see this since it's an old post, but I'm in the same boat, ITP after vaccination. For me it has now been over a year. I had the same question of whether vax-induced ITP might be shorter-lived, but unfortunately I'm still cytopenic. Currently my count is pretty good because I had dexemethasone a few months ago, but apparently this boost is usually temporary.
In my research I did come across
this study
that found antibodies were persistent as far as six months. What's annoying about these studies is they always have a set duration, so longer term follow-up is usually not available.
Promacta has some concerning side effects but it has been around a while and many people seem to have success with it. You could also look at Doptelet, which is a similar drug but milder side effects.
