Not that I'm disbelieving but are we talking life threatening - break out the epi reaction or just reaction? The reason I ask is because I see a ton of dogs in a year and often talk shots during intakes and I have met one, in my entire life where the owner said "got a combo vac with lepto and a rabies shot at the same time and the dog nearly died. No more shots for her." In fact I have probably vaccinated several thousand animals in my life between the barnyard, the kennels, the lot, and the farm and to my knowledge I can't think of one serious reaction in a sheep, goat, cow, cat, bird, horse, donkey, or dog. Feelin mildly under the weather yes, some swelling maybe, but not drop dead, blood pressure drop, throat swelling shut reactions.
I mean it's possible I've just gotten extremely lucky over the years but I thought I'd ask.