It is fairly common for horses and ponies to experience mild and temporary side effects after receiving a vaccination. These signs are all perfectly normal and are evidence that an immune response has been stimulated. Common side effects include:
localized muscle soreness and/or swelling,
loss of appetite,
lack of energy or alertness.
In rare cases, more serious side effects can occur. Over-reaction of the immune system may lead to:
Monitor your horse closely for the first few hours after it receives a vaccine or other immune stimulant. If you observe an abnormal reaction, call your veterinarian immediately. Vaccines are safe and efficacious when used as directed. If you have any questions, speak to your veterinarian.