Adverse Vaccination Reactions – What you Should Know
Every spring I administer well over a thousand vaccinations by deep intramuscular injection. I get less than 10 calls a year with reports of adverse vaccination reactions. In my 27 years of veterinary practice, I have seen 3 true allergic/anaphylactic responses to vaccination, and no other serious vaccination complications. Vaccination is a safe, effective way to protect your horse against disease. However, you should be familiar with adverse vaccination reactions, and understand their potential consequences.

By far the most common adverse reaction to vaccination is the simple sore neck. Typically the day after vaccination you notice that your mare is unwilling to move her head, and she exhibits pain and swelling at a vaccination site. Occasionally the discomfort will be so severe that horse will not lower their head to eat or drink, or will pull back if pressure is applied to a lead rope when they are haltered. These inflammatory reactions typically resolve within 48 - 72 hours with treatment including warm compresses, offering food and water a comfortable height, and administering non-steroidal anti-inflammatory medication.

This "sore neck" reaction is NOT an allergic response to the vaccine. True allergic responses occur immediately, or within minutes, of vaccination. Rather, these are exaggerated inflammatory responses to the ingredient in the vaccine that stimulates the horse's immune system. Called an adjuvant, this ingredient amplifies your horse’s response to the vaccine’s disease organism. The ideal adjuvant is a potent stimulator of the immune system but does not cause severe local soreness. Unfortunately, individual horses may respond unfavorably to the adjuvant in specific vaccine brands or antigen/adjuvant combinations.

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