Currently there are equine vaccines available for:

• Tetanus : injection of modified toxin (toxoid)
• Eastern, Western, Venezuelan Viral Encephalomyelitis : injection of killed virus
• West Nile Viral Encephalomyelitis : killed virus (Fort Dodge) / modified live canarypox vectored (Merial)
• Influenza, many different strains : injection / intranasal
• Herpesvirus-1 : abortion, respiratory, and neurological disease
• Herpesvirus-4 : respiratory disease and abortion
• Strangles : injection of killed bacterin / intranasal vaccine (Fort Dodge)
• Rabies : injection of killed virus
• Potomac Horse Fever : killed rickettsia
• Equine protozoal Myelitis (EPM): killed protozoan
• Botulism : injection of modified toxin (toxoid)
• Equine Viral Arteritis
• Anthrax
• Endotoxemia
• Rotavirus

With all the vaccines available there is probably no harder decision that a horse owner makes than what to vaccinate for and how often. Just a few of the problems with general recommendations is that:

• The incidence of these diseases differs in different parts of the world, different countries, and even smaller geographical areas.
• The efficacy and safety of these vaccines vary remarkably.
• Even your goals effect which vaccines you should use.

Often incomplete information is available on vaccine efficacy and safety. On top of all this, the equine news media makes each disease outbreak sound like impending doom for your horse and rarely question the safety, efficacy, or necessity of vaccination issues.

The bottom line is you only will want to vaccinate for those problems that occur locally, for which your horse is at risk for, and for which there are safe, efficacious vaccines. Even when these criterion are met there still may be some milder diseases for which vaccination is not prudent. The risk of many diseases can be greatly reduced by understanding how your horse contracts the disease and instituting preventive measures. This article discusses in detail the decision to vaccinate, how these vaccines work and don't work, vaccine safety and reactions. The vaccines themselves are listed and briefly discussed then linked to detailed articles on the disease and vaccines available. Links are also provided to specific vaccine schedules for different circumstances and articles on how to give vaccines.

Put is its simplest terms vaccines work by mimicking the presence of a infectious or toxic disease. The immune system senses the vaccine and then mounts a defense to the vaccine. The part of the vaccine the immune system senses is called an antigen and has to do with its shape and position of molecular electrical charges. The next time the immune system senses this antigen it mounts a quicker and stronger defense. Though infection occurs, this quicker and stronger defense may lessen or even prevent clinical signs from occurring.

Not all vaccines work the same. Many vaccines are killed disease organisms or are modified toxins called toxoids. Though killed or modified they still have some of the same surface shapes of the live organism or toxin and so prime the immune system for the real thing. Other vaccines are live organisms but are modified so they are less pathogenic, that is they do not cause serious disease. Viruses that are modified for vaccines are called modified live virus (MLV) vaccines. Bacteria would be called modified live bacterium (MLB) vaccines. Recently we have even seen more complicated scenerios where harmless viruses are modified so that they elaborate antigens to diseases we want to protect our horses from. The virus is introduced into the horse, it infects cells and elaborates the antigens producing immunity. These are called modified live virus vectored vaccines and currently there is a West Nile Virus vaccine that works this way.

Your first step to deciding what to vaccinate for starts with compiling a list of infectious diseases that occur in your area and areas where you travel. Certainly such a list starts with a talk with your local veterinarian but there are other resources. Your local extension service may have an equine specialist on staff and also your state veterinarian along with the veterinary diagnostic lab are good sources for this information. But the likelihood of contracting a disease is not the only factor in deciding what to vaccinate for. You should have the answer to these questions too:

• How serious is this disease?
• How well does the vaccine work?
• What is the frequency and seriousness of the side effects of the vaccine?
• Does protecting the horse also protect other horses or the horse owner from contracting the disease?
• Does vaccination result in persistence of the disease in the population?
• Does the vaccine create a diagnostic enigma or cause export restrictions?
• Does the vaccine create export or transport restrictions

You would think that just because a vaccine has had approval to be sold that it would be safe and efficacous but this is not always so. These factors vary widely from vaccine to vaccine and some of today's commonly used vaccines suffer from poor to moderate efficacy or relatively high reaction rates.

Consider your purpose for vaccination and also your philosophy. There are some horses that will go to any lengths to prevent disease in their horses while on the other side will be folks that economic considerations are very important in the decision making process. There is nothing wrong with introducing economic considerations into the equation, particularly where non-life threatening diseases or vaccines with low or questionable efficacy are concerned. But there are other reasons to not vaccinate for local diseases. For instance vaccination might:

• make a diagnosis more difficult, if it creates a titer that is picked up on serological tests.
• cause the use of resources (money mainly but time too) where they could be better used.
• creates an artificial sense of security preventing more effective preventive measures.
• Severe reactions are rare but can occur with any vaccine but is more tragic if the vaccine was unnecessary.

Almost everyone would agree that horses should receive vaccines for life threatening diseases that occur locally, that your horse might be exposed to, and for which there are efficacious vaccines. For most of the world this would include tetanus. Also most areas of the world are effected by one or more of the viral encephalomyelits diseases. As these are often transmitted by mosquitos or other wild vectors all horses where these disease are endemic are at risk. For the US and many parts of the world these would include Eastern and Western Viral Encephalomyelitis, West Nile Virus, and Rabies. South of the US border Venezuelan Encephalomyelits would be included. There are other viral encephalomyelits disease that occur in other areas for which vaccination would seem logical. These vaccines are inexpensive, effective, and have low reaction rates.

Which other disease you should vaccinate for will depend on your circumstances and by reading the articles on the particular diseases that are linked to below or following the guidlines set forth in the vaccine schedules also linked to below.