Core vs. Risk Vaccinations

As responsible horse owners, we know that every year we should vaccinate our horses against infectious diseases. With so many disease risks affecting our horses, it can be challenging to know what to vaccinate for, when to vaccinate and how often. As many equine diseases can vary by season and region of the country, consulting a veterinarian is the best option for ensuring a safe and effective vaccination program.

Courtesy AVMA

Vaccinations are broken down based on core vs. risk-based diseases. According to the American Association of Equine Practitioners vaccination guidelines, core vaccinations are those ?that protect from diseases that are endemic to a region, those with potential public health significance, virulent/highly infectious, and/or those posing a risk of severe disease1.? Alternatively, risk-based vaccinations may vary regionally, from population to population within an area, or between individual horses within a given population2.

Core Vaccines

Core vaccines have demonstrated efficacy and safety and a high enough level of patient benefit with a low enough level of risk to justify their use in all equids3. The following diseases fall under the category of core vaccinations that every horse should receive at least annually.

  • Eastern equine encephalomyelitis (EEE) and western equine encephalomyelitis (WEE): Both EEE and WEE are caused by mosquito-borne viruses. Both diseases produce severe, life-threatening neurologic disease characterized by staggering, tremors, dementia, seizures and even death. Exposure occurs wherever mosquitoes are present. All horses are at risk3.
  • West Nile virus: A viral encephalitis causing symptoms similar to WEE and EEE. The disease is spread by mosquitoes that have recently fed on an infected bird. Birds are the natural host of West Nile virus. Horses cannot transmit West Nile to humans or to other animals. Exposure occurs wherever infected mosquitoes are present. All horses are at risk3.
  • Tetanus: Caused by a soil-borne organism, Clostridium tetani. Tetanus is a life-threatening disease characterized by severe muscle paralysis and is often contracted through a wound, most commonly a deep puncture, but can occur whenever a horse experiences a laceration or abrasion. Bacterial contamination of the umbilical cord of a newborn foal is also a common route of tetanus infection. All horses are at risk3.
  • Rabies: An invariably fatal neurologic disease. The virus that produces rabies is shed in the saliva of a rabid animal. Rabies is also a human health exposure risk, as a rabies-infected horse can transmit the disease to a human. Common carriers of rabies in the United States include: opossums, skunks, bats, raccoons and foxes. However, any mammal may become infected with and thus transmit rabies. All horses are at risk3.

Pfizer Animal Health?s extensive equine product portfolio offers a complete line of vaccines for protection against both core and risk-based diseases. The core vaccines include WEST NILE-INNOVATOR?, to help protect against West Nile virus -? one of the most devastating health threats to U.S. horses today. In addition, the Mosquito Shot ? (WEST NILE-INNOVATOR? + EWT) helps protect against eastern equine encephalomyelitis, western equine encephalomyelitis, West Nile and tetanus in a single vaccine. INNOVATOR vaccines are also available in a variety of combinations.

Risk-Based Disease

Some horses may be at higher risk of particular diseases by virtue of age, geography, housing or function3. Also, not every horse will be exposed to every disease. Risk-based disease vaccination planning requires the input of a veterinarian familiar with your horses and their use.
The diseases that are categorized as risk-based include:

  • Anthrax: Anthrax is a serious and rapidly fatal disease caused by Bacillus anthracis. The disease is acquired though ingestion, inhalation or contamination of wounds by the soil-borne spores of the organism. Anthrax is encountered only in limited geographic areas where alkaline soil conditions favor survival of the organism4.
  • Botulism: Botulism is a highly fatal, rapidly progressive neurologic disease caused by toxins produced by Clostridium botulinum. The toxin can be ingested in contaminated feed, through an overgrowth of bacteria in the gut (known as Shaker Foal syndrome) or through wound or umbilical cord infections. The disease may be prevented in foals in high-risk areas through vaccination of pregnant mares3.
  • Equine herpesvirus (Rhinopneumonitis): Equine herpesvirus (EHV) can cause three forms of the disease: respiratory, abortion in mares and neurological. The neurologic and abortive forms of the disease are typically caused by EHV-1, while either EHV types 1 or 4 can produce respiratory disease. There is no specific vaccine against the neurologic form of the disease. EHV is transmitted from horse to horse through contact from fluids and by air transmission3.
  • Equine viral arteritis (EVA): EVA is caused by the equine arteritis virus and is primarily a reproductive concern, as it can cause abortion in pregnant mares, death in young foals and a permanent carrier state in stallions. Although many exposed horses will develop no disease signs, when clinical disease does develop, it manifests through: fever, swellings (legs, sheath, scrotum, udder and around eyes), loss of appetite, depression, conjunctivitis, nasal discharge, rash, abortion in mares, pneumonia/death in foals and short-term sub-fertility in stallions3.
    EVA infection is transmitted through: respiratory secretions, venereal contact, indirect contamination (tack, equipment, hands, clothing) and across the placenta from mare to foal. Infected (sexually mature) colts and stallions may become permanent carriers of the virus and shed it in their semen. Because this carrier state depends upon the presence of male hormones, geldings, mares and immature colts cannot become carriers3.
  • Equine influenza: Equine influenza virus (EIV) causes an upper respiratory disease characterized by fever, malaise and upper respiratory symptoms, such as nasal discharge. Flu can result in days missed from training or performance and can make the horse vulnerable to opportunistic pathogens that can cause pneumonia3.
  • Potomac Horse Fever: Caused by Neorickettsia risticii, equine monocytic ehrilichiosis was originally associated with the geographic region surrounding the Potomac River. However, the causative organism has been found in horses from California, Illinois, Indiana, Kentucky, Maryland, Michigan, New York, New Jersey, Ohio, Oregon, Pennsylvania, Texas and Virginia. Signs of the disease include: fever, diarrhea, laminitis, mild colic and decreased abdominal sounds. Pregnant mares can abort if infected at 7 months gestation3.
  • Rotavirus: Rotavirus, a non-enveloped RNA virus, is a major infectious cause of foal diarrhea and has been documented to cause 50 percent or more of foal diarrhea cases in some areas5.
  • Streptococcus equi (Strangles): Strangles is a highly contagious respiratory disease, typically characterized by high fever, profuse nasal discharge and abscessed lymph nodes (usually under the jaw). S. equi can also cause internal abscesses ? in the lungs, liver or lymph nodes in the abdomen. This internal form of the disease is commonly called ?bastard strangles? and can be life threatening and difficult to treat. S.equi can also lurk in the guttural pouches of the horse, causing an apparently symptom-free horse to be a carrier. Over-sensitization to the S. equi antigen can cause a severe auto-immune disease called purpura haemorrhagica. Strangles is highly contagious, passed through direct contact with nasal secretions or abscess fluid from an infected horse, through aerosolization and through objects such as brushes or hands that have contacted infected materials3.

EVA is passed by direct horse-to-horse contact but can be transferred through indirect means such as shared equipment and handlers. Arm yourself with knowledge. Download AQHA?s FREE EVA: A Manageable Problem report today.

Pfizer Animal Health?s broad vaccine portfolio also includes a number of products that help protect against equine risk-based diseases. Among the risk-based vaccines is FLUVAC INNOVATOR? EHV-4/1, which helps protect horses from equine influenza and also contains both EHV-1 and EHV-4 vaccines to help protect against rhinopneumonitis. Also available is ARVAC?, the equine arteritis vaccine, PINNACLE? I.N, the Streptococcus equi vaccine for protection against strangles and the equine rotavirus vaccine*. These are just a few of the vaccines available in the Pfizer Animal Health vaccine portfolio, so be sure to consult your veterinarian about the options available for your horse.

The INNOVATOR vaccines, along with other Pfizer Animal Health equine vaccine combinations, are included in the Equine Immunization Support Guarantee. The Pfizer Animal Health Equine Immunization Support Guarantee provides up to $5,000 for reasonable diagnostic and treatment costs if a horse properly vaccinated by a veterinarian contracts the corresponding equine disease. Disease protection backed by the Equine Immunization Support Guarantee includes infection from West Nile virus, equine influenza virus, tetanus, eastern equine encephalomyelitis virus, western equine encephalomyelitis virus and Venezuelan equine encephalomyelitis virus. Vaccinations must be performed by a licensed veterinarian with an established client-patient relationship to be eligible.

Remember, keeping vaccinations straight can be challenging for even the most seasoned equine professional. Your veterinarian is your best ally for helping to keep your horses healthy and performance-ready.

* This product license is conditional. Efficacy and potency test studies are in progress.


1. Core Vaccination Guidelines. American Association of Equine Practitioners. 2008. Available at: Accessed on January 24, 2012.

2. Risk-Based Vaccination Guidelines. American Association of Equine Practitioners. 2008. Available at: Accessed on January 24, 2012.

3. Equimed 2012 Vaccination Guidelines. EquiMed?. August 30,2011. Available at: Accessed on January 24, 2012.

4. Anthrax. American Association of Equine Practitioners. 2008. Available at: Accessed on January 24, 2012.

5. Rotaviral Diarrhea. American Association of Equine Practitioners. 2008. Available at: Accessed on January 24, 2012.

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