I promised to let you know how our Olly got on. Very sadly he went back to the vets who confirmed our worst fears. He had become so very ill so quickly, the drug treatment didn't work and he just wasn't Olly, not eating, moving or able to stand. It was the hardest thing we have had to do but we had him put to sleep. The vet said any further treatment or tests would just confirm exactly what it was, not make him better. The vet who has been treating him was lovely and we ended his suffering, I suppose we should be grateful it was only for a week. We are convinced the booster was either the reason or certainly triggered something underlying (most likely a problem with his bone marrow) and in future I shall encourage pet owners to look into the two arguments so they can make an informed choice. Another vet there was so ridiculosly over defensive at the vaccine issues we presented, it makes you wonder. Thanks to your comments we ended up doing alot of research on this. We miss him so so much and can't imagine life without him. I never imagined I would have to send this reply and find it so hard but I know if I had read this I would have wanted to know what happened. Thanks again for all your kind words and advice.