However, since there apparently have been no studies done on the longevity of protection provided by the specific vaccines, and because some vaccines do occasionally cause unpleasant side effects, and because there is the possibility that overly aggressive vaccination regimens are a factor in the development of auto-immune problems, and because my animals stay at home with little or no contact with animals off this property, I have decided to vaccinate the horses only for those diseases which are usually fatal. This year I vaccinated for tetanus exclusively. I intended to switch to an every-3-yr schedule for EW encephalomyelitis, but I think I've changed my mind about that. I live in one of the mosquito capitals of the country, and I think it's probably safer to vaccinate for EW on a yearly basis as I have always done in the past. I have never vaccinated for rabies, though I have often considered doing so. Perhaps I will do that as well, but not more than once every 3 yrs. So, until I change my mind again or read more knowledgeable information and studies on the subject, or until they develop safer and more efficacious vaccines, or unless my horses' exposure to other equines increases, I will vaccinate my horses once a year for tetanus and EW, and once every 3 yrs for rabies (maybe).
I'm not sure what I'd do in your situation where your horse is exposed to other horses half a dozen times a year. I suppose that depends on which diseases he's been exposed to, contracted and developed a natural immunity to already; which diseases are endemic to your area; and how much of a problem it would cause you and your horse if he did get ill for a while with a non-fatal disease. There doesn't seem to be any question that a horse develops a stronger and more thorough immunity through natural exposure to disease, but you must certainly consider the physical consequences of such exposure and potential subsequent illness (including possible abortion in pregnant mares). Then there are the issues of efficacy of each of the vaccines you're using, common and uncommon side effects, and cost. These are all matters for you to weigh in making a choice for your horse's vaccination regime and schedule.
If I were considering vaccinating for a number of different diseases, and since I administer my vaccines myself, I would be inclined to spread out the vaccines over a period of several weeks and avoid using combination vaccines in lieu of single vaccine formulations. Although I may well be wrong about this, my gut instinct is that such an approach might help avoid some adverse reactions.
I'm sorry I'm not able to give definitive answers and recommendations here. This is an area of continuing research and discussion. The best I can offer is the suggestion to talk all of this over with the best equine veterinary specialist you can find and then make the most informed decision you can based on your own horse's situation. In addition to the fine Equus articles already mentioned, you can find more information on vaccines at the following URL:
Q. What are your thoughts regarding vaccinations? Specifically, what vaccinations do you recommend and at what intervals? Do you recommend single vaccines or combination vaccines? Recently, there were pro/con articles about this subject in Equus, and I was surprised to read about the negative consequences of vaccinating - most importantly, that repeated and frequent vaccinations can actually break down the immune system. The article went on to say that if a horse has allergies and sarcoids, his immune system is already compromised and not to subject the immune system to repeated and unnecessary vaccine assaults. My horse has respiratory allergies and one sarcoid. I'm considering switching my horse's vaccinations to once a year. In the spring, he received Potomac/Tet/EW Enceph, flu/rhino, and rabies. Is there a need to repeat any of these in the fall? What are the efficacies? He lives on my property with one other horse and travels locally maybe six times a year. Any advice?
A. This is an excellent question and a very volatile subject open to much speculation among veterinarians, researchers, and animal owners alike. This spring is the first time I started hearing anything about the efficacy vs. potential risks of overvaccinating pets, including horses. I have not researched this subject extensively myself, but I have read enough (including the articles you mentioned in the June 1998 issue of Equus) to cause me to re-evaluate my vaccination schedules. There is so little hard evidence or research concerning this issue in the veterinary pharmaceutical community, owners are left up to their best informed guess at the moment. Some vaccines are known for providing very low percentages of efficacy and/or considerably higher incidences of adverse reactions. We don't know how long adequate immunity is provided by even the more effective vaccines. Heck, we don't even know what constitutes adequate immunity! We don't know if there is any actual correlation between overvaccinating and the development of auto-immune diseases. (I see it as just as likely that all the environmental toxins and pollutants we've inflicted upon this planet are causing equally toxic effects in the earth's inhabitants) We don't know if potential adverse reactions to vaccines are caused by the disease antigens or by the adjuvants added to the vaccines. It would seem we don't actually know much of anything other than the fact that the use of vaccines has dramatically decreased the incidences of the diseases against which they're designed to provide protection.
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