The FDA gave Fort Dodge a conditional license for its EPM vaccine based on the company’s initial laboratory work. This means the vaccine’s use is limited to veterinarians and only in states that approve its use (the state veterinarian has to say OK).
Technically, the research to prove safety and efficacy isn’t finished on the vaccine — veterinarians must report any reactions or problems to the FDA — but the FDA found Fort Dodge’s work sufficient enough to make the vaccine available on a limited basis under the circumstances. EPM treatment protocols are extremely expensive with no real guarantees the horse will recover, so prevention through a vaccine is attractive and Fort Dodge’s vaccine is the only available option.
Opposition to the vaccine centers on the belief that it is unproven, but this isn’t an unusual furor surrounding any new vaccine. Of particular importance with this one, however, is that vaccines developed along similar lines for other protozoal diseases have failed to provide protection. Fort Dodge has shown that animals given the vaccine do respond by producing antibodies. The problem is, horses with EPM also have plenty of circulating antibodies. An antibody response is no guarantee the horse will be protected from developing the disease.
Until someone finds a way to predictably induce the disease in experimental animals — so the vaccine can be tested for its ability to actually prevent symptoms — we believe the question of whether or not this vaccine actually protects against EPM will remain unanswered.
On the safety front, there’s concern about what might happen if you give the vaccine to a horse that is already harboring the organism or in the early stages of the disease. Others point to the remaining mysteries surrounding EPM itself and how great a threat it really is, arguments that may have merit. The one thing research has proven about EPM is that it is not consistent — some horses get it and some don’t. While it’s long been believed to be transmitted to horses via opossum feces, there’s evidence that other animals may also be hosts to the protozoa and that other types of protozoa may be involved. Symptoms of the disease can progress rapidly or even diminish spontaneously. They are also often similar to other neurological diseases.
If you’re considering the EPM vaccine, discuss it carefully with your veterinarian. EPM can be horrible, but we feel the actual incidence of the disease is relatively low. While this vaccine may be a step in the right direction, we believe it has a long way to go to prove it is truly effective and safe.
’Til Next Month,