Personally would never consider a mating without using it...have had 4 litters using the vaccine since its introduction in 2003. twice with the same bitch. Excellent healthy litters each time, good sized pups. althoug I did lose a couple of pups, none of the problems related to the vaccine.... personally have not heard of any defects or abnormarlities attributed to the vaccine....although there may be some.
After having litters with FPS and all it entails....I would have to say that the pro's vaccine far outweighs any possible con's
Have a read of the following link.....I wrote this back in June last year...Hope it helps put your mind at rest..
http://www.champdogsforum.co.uk/cgi-bin/board/topic_show.pl?pid=524500;hl=CHV%20;hlm=and#pid524500