2015 I am removing this post. The reaction was found to have happened as a result of the particular single batch being bad - something that can happen to milk or anything with a shelf life that is subject to poor handling.
This post has been viewed far too many times recently and I simply have no wish to fuel the anti-vax mentality. I vaccinate all my animals & myself for the sake of us all.
You can have a reaction of the worst type to a bee sting too. Always use veterinary professionals (one on hand saved this mare's life) and don't buy discounted drugs if you vaccinate yourself, or have them shipped cheaply. The company making this drug paid for the animal's treatment as I understand it (although it's possible handling of the vax after it left them was the cause)...and she lived a long time after this event, well into her 30s.
Vaccinations still save lives.