A to-the-point discussion with Dr. Dennis Rach of Moore Equine Veterinary Clinic, Balzac, Alberta.
Q. Recently there appears to be a fair amount of literature surfacing on the internet regarding the potential “over-vaccination” of our horses. Can you comment on this at all?
DR – There are people who have decided that vaccines are poison, etc. The fact is that influenza vaccine is only effective for a period of time. Intramuscular influenza vaccine elicits an immune response that elevates the antibody level to a point above the known protection level for a little over six months. That is why show horses should need two flu shots a year. Since most flu cases appear in the spring and not the fall, we usually vaccinate in the spring to be able to give it to horses just before they start to go out and come into contact with others.
Rhino is somewhat the same but the protective immunity level is “somewhat protective” for two or three months. The reason we give the rhino vaccines at stables is because we think it reduces virus shedding by carrier animals. Mosquito-borne virus vaccines elicit protection for 10 to 12 months and so annual vaccination is adequate.
Potomac horse fever (PHF) vaccine is given twice a year in endemic areas but in Alberta we only see it from August through October and so we vaccinate high risk areas for PHF late spring or in the summer. There is more PHF found east of Calgary in the irrigation areas than west of the city, so many people west of Calgary do not vaccinate. They feel the incidence is low enough to take the risk of not vaccinating.
Strangles vaccination seems to be protective against the Strep-equi strain for around 10 months and so we also do it annually. However, if a horse gets the disease naturally and recovers from Strangles, the affected horse usually has protection against the disease for three years or so. Therefore, these horses do not need immunization during that time. The death rate in a stable with a strangle outbreak on average, is around 3 to 5% of that population.
Tetanus and rabies are effective for several years so if the tetanus toxoid was not already in the sleeping sickness vaccines, we would not vaccinate for it but every four or five years.
In short, most of the respiratory vaccines do not elicit a lengthy enough response to be protective for more than a year. After that time period, horses who have been challenged with live virus get sick. Clinical trials on vaccines have been done to determine the degree of protection – their purpose is to essentially work out vaccination protocols and discover how often we have to vaccinate, to achieve and maintain protection.
* Be sure to check out the upcoming April issue of Western Horse Review! In it you will find a comprehensive article on vaccinating your horses for 2013.