Colorado State University Statement About West Nile Virus Vaccine and Pregnant Mares

Note to Editors: In response to widespread erroneous reports inadvertently picked up by AP West Wire and being reported by local and regional news organizations, and in a continual effort to provide the public with accurate information for decision making purposes, veterinarians at the Veterinary Teaching Hospital and the College of Veterinary Medicine and Biomedical Sciences at Colorado State University are issuing the following statement regarding the university’s position on West Nile virus vaccine and pregnant mares.

Since the incorrect information began being reported on June 16, the College of Veterinary Medicine and Biomedical Sciences has received dozens of calls from reporters, concerned veterinarians and horse owners throughout Colorado and the West. This statement is meant, in part, to address those concerns.

Colorado State University neither provided nor approved the incorrect information that was reported earlier this week.

In contrast to incorrect accounts widely reported earlier this week, veterinarians and researchers at the Veterinary Teaching Hospital and the College of Veterinary Medicine and Biomedical Sciences at Colorado State University have not forwarded any adverse reaction reports of troubled births caused by pregnant mares receiving the West Nile virus vaccine in their practice to the USDA, the state veterinarian or Fort Dodge, the manufacturer of the vaccine.

Furthermore, no members of the college’s equine field service team, equine reproductive laboratory or other equine veterinarians have personally observed pregnancy loss, early or late, or deformed foals, attributed to the WNV vaccine.

Colorado State University veterinarians are continuing to suggest to their clients that vaccinating equids according to the manufacturer’s recommendations is one important step toward preventing WNV disease in horses. Colorado State University veterinarians recommend that mare owners should work with their veterinarian to determine the best plan for their horses regarding vaccination against WNV as well as to develop a complete disease prevention plan.

Along with several other veterinarians throughout the nation who are speaking out about the concern, Colorado State researchers report not having personally witnessed WNV vaccinations causing problems in pregnant mares.

Colorado State University veterinarians acknowledge, however, that there have been concerns from a group of mare owners who feel the WNV vaccine has caused abortions and deformations in foals. Colorado State University veterinarians have always encouraged horse owners and veterinarians to report any concerns they have with a vaccine or drug to the manufacturer and the appropriate federal licensing agency. Fort Dodge, the manufacturer of the WNV vaccine, is investigating the reports of foal loss in mares vaccinated with the WNV product and the USDA Center for Veterinary Biologics has launched an investigation into the reports. Colorado State veterinarians do not have adequate scientific information on these reports to make any kind of judgment and plan to await the USDA Center for Veterinary Biologics report. Once the USDA Center for Veterinary Biologics report is completed, Colorado State veterinarians will determine if the university’s WNV vaccination practices or policies need to be revised.

Colorado State University veterinarians suggest that horse owners or veterinarians with concerns regarding WNV vaccine and pregnant mares should contact the USDA’s Animal and Plant Inspection Service (APHIS) Center for Veterinary Biologics at (800) 752-6255 or via the Web at University researchers further state that horse owners or veterinarians who believe they witness adverse equine reactions to any vaccine should report the incidence to the manufacturer and the USDA’s Center for Biologics.

Results of a recent study at Colorado State University show that Colorado reported 378 and Nebraska reported 1,100 confirmed cases of WNV last year in equids. The estimated case fatality rate for affected equids in Colorado and Nebraska in 2002 was 28.6 percent, similar to reports from other regions of the United States.

Only 13 cases in the study were fully vaccinated based on current recommendations from the vaccine manufacturer, meaning they had two vaccinations separated by three to six weeks followed by adequate time for the vaccine to be fully effective before the arrival of vector season. Of these, the survival status of 12 is known and all 12 lived. However, even infected horses that had not received both prescribed doses of vaccine several weeks prior to exposure to West Nile virus were more likely to survive than those that were non-vaccinated.

While vaccination reduces the chance that an animal will contract disease if exposed to the West Nile virus, it does not completely protect all fully vaccinated horses under field conditions. The Colorado State researchers state that it is important for equine owners to employ other strategies for prevention of the disease including mosquito mitigation.