I've used the Zoetis Core vaccine multiple times for Mill and Jack without incident. It's called Core because is covers the vaccines a horse needs even if it never steps a hoof off the home property (Eastern & Western Encephalomyelitis, West Nile, Tetanus and Rabies). Several years ago I spoke directly with a Zoetis equine rep about reactions. She said the number was exceptionally small despite the number of doses administered. I don't remember the exact percentage. Their website says 99.7% reaction free, but that doesn't help if your horse is the 0.3%.
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Jennifer in Middle TN  2010
 Mill 33 1/3 yrs Arabian-PPID, IR & Pacemaker Dependent; 2-13-89 to 6-11-22
Jack 23 yrs TN Walker- IR & RAO

https://ecir.groups.io/g/CaseHistory/files/Jennifer%20and%20Millionairess

https://ecir.groups.io/g/CaseHistory/album?id=831

https://ecir.groups.io/g/CaseHistory/files/Jennifer%20and%20Jack-TN%20Walker