Could Your Horse's Vaccines Be Causing Harm?

The question of which vaccines your horse needs and how often to vaccinate him/her is complex. There is a growing debate on this important topic.  Are horse’s being over vaccinated, and is this causing harm?

Last week’s publication of a research study conducted by Oregon Health & Science University (OHSU), (a world renowned hospital and research center), suggested that adults only need a tetanus shot every 30 years, not every 10 years as is current practice.  In their paper, the researchers stated there was very little data to prove or disprove the current “every 10 years” practice.  Study data indicated adults remain protected for at least 30 years. 

This research study and the fact that there are few, if any, vaccines that are recommended annually for humans (and equine and human immune systems function the same way) got me thinking, once again, about all equine (and canine) vaccinations, not just tetanus.  Why are most horses vaccinated annually for the “core 4” if not more?  Is there data to support this vaccination schedule?

Current Guidelines
Let’s take a step back.  The American Association of Equine Practitioners (AAEP) guidelines suggest most horses should be vaccinated annually for Tetanus, Eastern/Western Equine Encephalomyelitis, Rabies and West Nile Virus.  Additional risk-based vaccines may also be given such as Strangles, Flu, EHV and Potomac Fever to name a few.  Of course, the AAEP guidelines state that vaccine decisions should be made in consultation with the owner’s vet, though a majority of horse owners and vets follow the AAEP recommended guidelines.   

How Do Vaccines Work?
Here is a quick, high level and easy to understand overview of how vaccines work provided by the Centers for Disease Control (CDC).

1) What is Immunity?

When disease germs enter your body, they start to reproduce. Your immune system recognizes these germs as foreign invaders and responds by making proteins called antibodies. These antibodies’ first job is to help destroy the germs that are making you sick. They can’t act fast enough to prevent you from becoming sick, but by eliminating the attacking germs, antibodies help you to get well.

The antibodies’ second job is to protect you from future infections. They remain in your bloodstream, and if the same germs ever try to infect you again — even after many years — they will come to your defense. Only now that they are experienced at fighting these particular germs, they can destroy them before they have a chance to make you sick. This is immunity. It is why most people get diseases like measles or chickenpox only once, even though they might be exposed many times during their lifetime.

 2) Vaccines to the Rescue

Vaccines offer a solution to this problem. They help you develop immunity without getting sick first.

Vaccines are made from the same germs (or parts of them) that cause disease; for example, polio vaccine is made from polio virus. But the germs in vaccines are either killed or weakened so they won’t make you sick.

Vaccines containing these weakened or killed germs are introduced into your body, usually by injection. Your immune system reacts to the vaccine the same as it would if it were being invaded by the disease — by making antibodies. The antibodies destroy the vaccine germs just as they would the disease germs — like a training exercise. Then they stay in your body, giving you immunity. If you are exposed to the real disease, the antibodies are there to protect you.

Why Are Vaccine Boosters Needed?
A single dose of some vaccines provides lifelong immunity to most people, while other vaccines require additional doses, i.e. a booster, in order to maintain immunity.  Sometimes boosters are needed because the immune response “memory” weakens over time.  A booster is like a reminder to the body’s immune system.
Vaccine Reactions
Vaccines can cause reactions in humans and in horses.  Reactions to vaccines can range from very minor to severe and life-threatening.  Equine vaccine reactions can include, but are not limited to:
  • Injection site swelling—for days, weeks or even months
  • Fever
  • Lethargy
  • Lameness
  • Swelling in the limbs
  • Muscle stiffness and soreness
  • Anaphylaxis  (rapidly advancing life-threatening allergic reaction)
Some of these reactions can require extensive treatment and convalescence, while others dissipate on their own.

Are Annual Boosters Needed For Horses? What is the Scientific Data Supporting This Schedule? 
Many vets firmly believe that annual vaccination is necessary. However, there is curiously little research data to support this schedule which is unfortunate.  More research funding is needed.

In recent years, there has been a small but growing number of vets (and horse owners) that are rethinking the annual vaccine protocol.  This is due to mounting evidence that over vaccination is a problem due to the increasing number of negative side effects, some of which can be permanent, broadly called vaccinosis.

Here are links to 4 articles from vets who are rethinking the annual vaccination protocol.
Rethinking Vaccines, By Dr. Joyce Harman
Vaccination Protocol, By Dr. Mark Depaulo
Rethinking Vaccines, By Dr. W. Jean Dodds (article part one)  (article part two)

Each article offers a detailed explanation regarding how vaccines work, as well as the benefits, risks and side effects. They all also discuss the lack of data supporting the annual guidelines and suggest alternative ideas regarding the timing of vaccines, which vaccines to vaccinate for and titers testing.  Titers testing is a laboratory test measuring the existence and level of antibodies to a disease in the blood. Antibodies are produced when an antigen (like a virus or bacteria) provokes a response from the immune system. This response can come from natural exposure or from vaccination.  The amount and diversity of antibodies correlates to the strength of the body's immune response.  That said, titers teting has limitations and a positive or negative titers test is not a clear cut answer as to whether your horse or dog is protected.

Some Questions to Consider When Deciding on A Vaccination Schedule and Consulting with Your Vet
  1. Is your horse a performance horse that attends a lot of shows/events, or more the stay-at-home type?
  2. Does your horse have their own acreage with a small number of stay-at-home horses, or is your horse boarded at a big facility where there’s more risk of exposure?
  3. How old is your horse?
  4. How is your horse’s overall health?
  5. What diseases are prevalent in your area?
  6. Has your horse had a previous vaccine reaction?
Bottom line....
My purpose in writing about current common vaccine practices and thoughts is to enable a healthy debate and free exchange of information so each horse owner can make an informed decision about what is best for their horse’s health and well-being.  Vaccines can be a very beneficial tool to fight disease.  I am in no way suggesting that horse owners should stop vaccinating their horses.

There is no one size fits all answer as to how often your horse needs to be vaccinated and with what vaccines.  Sadly, there is little research on this complex issue.  So, stay informed on this topic and talk to your vet and other vets too!

What is your opinion?  Do you think horses are being over vaccinated?  Why or why not?  Has your horse ever had a bad reaction to a vaccine? 

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