death of rabbit after calisi virus injection

Question
I took my rabbit (dwarf lop)to the vet for a checkup as he had been on antibiotics for an ear infection. He had greatly improved. he was happy today and came up to me for a cuddle. bu t before I left I reminded the vet for my rabbit's yearly calisi vaccination, of which he gave it to him.(my rabbit was 4.5 years  old and had the vaccination every year). I drove home and he went to his usual part of the house.About one hour later I saw him on the floor trying to move himself by the back legs(in other words he could not walk).My daughter picked him up and his heart was beating fast.I rang the vet and took him there. on the way, my daughter saw him closing his eyes and his heart slowing down. when we arrived at the vet, he took the rabbit with him to the back. he came back saying that our beautiful rabbit had passed away. He injected adrenaline into his heart but it was too late.He has had no experience of a rabbit dying from the injection. he has used the same batch on other rabbits with no problems.The vet can't explain what brought about his death (he had a heart attack).How can a healthy rabbit die suddenly from such an injection (given that he has had three injections in the last 3 years with no issues).Could you please shed some light/
Many thanks,
Tony

Answer
Dear Tony,

I am so sorry about the terrible tragedy your family suffered.  

It is very strange that he should have a reaction to the injection more than an hour after the shot.  If there is to be an anaphylactic (allergic) reaction to the serum in which the vaccine is delivered, it usually happens relatively quickly after the injection.

There is a possibility that this was not directly related to the vaccination, though the coincidence would certainly lead one to suspect this.  It is possible that your bunny suffered an embolism or some other silently deadly disorder that took his life.  Even a necropsy might not reveal this, and it is too late for that now.

One cannot be sure he had a heart attack as the primary cause of death.  In fact, cardiac arrest might have simply followed a general anaphylactic reaction as a matter of course.  This type of situation is very rare, but not impossible.

I am so very sorry.  

Sincerely,
Dana