FAQ – Vaccine Reactions

By Dr. Nolfi

Vaccinations are a part of horse ownership. In the US, we have core vaccines (ones all horses should
receive) and risk-based vaccines (ones that are given based on endemic disease rate, housing situation of the horse, exposure of the horse to other horses, etc). Have a look here for more information about vaccines: https://aaep.org/guidelines/vaccination-guidelines

Vaccinations can have side effects, which are relatively common, and they also can have reactions,
which are rare.
Side effects are to be expected with any vaccination – in any species. Swelling, pain at injection site,
bruising, and mild to moderate effects of the pathogen being vaccinated for – these are all side effects, no matter how mild or severe. Some individuals are more susceptible to side effects. For example – some people have more swelling at the site of administration of a flu vaccine than others, and some people might even feel a little “flu-ish,” while others feel nothing. Horses are the same. Some have significant swelling, may become depressed, reluctant to move and off feed, whereas others have minimal side effects.

It is difficult to know who will have minimal to no side effects versus who will have moderate side
effects, until it happens. Once we know that a horse is more likely to develop side effects that interfere with daily life, then we will premedicate typically with an NSAID such as flunixin meglumine (Banamine), which helps to mitigate the side effects. There is some thought that administration of an NSAID at the time of vaccination may actually dampen the immune response to the vaccine – but – if the side effects are such that the horse goes off feed and is miserable, then we give it for sure (same as humans). We also use flunixin as a treatment for side effects, after they have occurred.

A vaccine reaction is a different event. This is an anaphylactic reaction and if this occurs – it’s a lifethreatening emergency as in any other species. We don’t typically administer antihistamines to horses prior to vaccinations – but – that’s not to say that it is never done – and if a horse is known to have severe side effects and we must administer a vaccine, it wouldn’t be a bad idea. When a horse has severe side effects, we have discussions about pros versus cons of vaccinating.

Side effects of vaccines:

• Mild fever (up to 102.0 F)
• Mild swelling at the injection site(s)
• Muscle soreness
• Mild malaise (lethargy)
  
  Reactions to vaccines:
  
• Moderate to severe fever (over 102.0 F)
• Severe swelling
• Difficulty breathing
• Colic – discomfort, diarrhea, lack of manure production
• Laminitis
• Purpura hemorrhagica
• Hives
  
  Veterinarians should report all adverse reactions to the vaccine’s manufacturer. Adverse events may
  also be reported to the USDA Center for Veterinary Biologics at (1-800-752-6255) or through the
  agency’s web site: https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/veterinary-biologics
  
  If your horse is experiencing side effects of vaccines:
  
• Ring the veterinarian that administered the vaccines
• Cold compress swollen areas
• Elevate feed/water to make it easier to eat/drink
  If your horse is experiencing a vaccine reaction:
• Ring the veterinarian that administered the vaccine or an emergency veterinarian immediately
  Prevention of recurrence of side effects:
• Discuss the vaccination schedule with your veterinarian prior to the next administration time.
  o Discuss core vs risk based vaccines, endemic disease, and likelihood of infection
• Discuss titers for vaccines. Realize that we do not know protective titers for all diseases, titers
  only test one arm of the immune system, and may not give a complete picture of immunity.
  o See the AAEP Guidelines for Serologic Testing of Vaccine Titers for more information:
  https://aaep.org/sites/default/files/Documents/AAEP_Serology_Guidelines_Final_10.26
  .20.pdf
• Discuss splitting the vaccines into a few antigens at a time to determine which vaccine the horse
  is reacting to – however, most often it is the adjuvant in the vaccine vs the antigen itself.
• Discuss changing manufacturers of the vaccine (manufacturers use different antigens).
• Discuss administration of NSAIDs prior to vaccinating the horse.
• Discuss changing the location where the vaccine is administered – neck vs pectorals vs back of
  the leg (never the top of the leg/hip area).
• Ensure the vaccine is at body temp just before administering.
• Discuss changing needles to a silicone-free needle as some horses react to the needle itself vs
  the vaccine.
  
  See also: https://lookaside.fbsbx.com/file/Vaccines%20-
  %20Veterinary%20Administration.pdf?token=AWygQQfjh9mdbkze4dY7b_TZtcIxztXVf5jAhIT4lassAYbSqeTpqiVTq3lmwhgv8067jCLgO9jEDM8Y4PJc77mn0-
  7bEBMHyasphsmBZhA93l03CVTIs_YiG0ZEzxtHf_UJczSWioOVtFI3IeZMzhCps8z9BhbCTchfBojBYnGcg