Vaccinating Strategically

Every spring, you ask your veterinarian to vaccinate your horse to protect her from disease while she's showing, racing, carrying a foal, or hanging around your pasture. But is this yearly routine the best way to confer immunity with the vaccines currently available?

Hugh Townsend, BSc, DVM, MSc, a professor in the Department of Large Animal Clinical Sciences at the Western College of Veterinary Medicine, University of Saskatchewan, addressed the issue of strategic vaccination on June 12 at the 22nd annual conference of the American College of Veterinary Internal Medicine in Minneapolis, Minn. He suggested that it's time to move away from the idea of routine yearly administration of vaccines and consider vaccinating to achieve the greatest protection in periods of high disease risk.

"Vaccines are very specific tools, and they have limitations that we have to keep in mind when designing vaccination programs," he said. "Vaccines for infectious respiratory diseases, particularly, need to be administered with the efficacy of the formulation and the risk periods for the disease in mind. If you don't match duration of immunity with the risk period, you may not get the best out of the vaccine."

Townsend admits, "There's a lot we don't know about the duration of the effectiveness of the vaccines available to us. And we don't really know what level of protection is sufficient, either--you can't just establish a titer of a certain level and say, 'that horse is protected from disease and this one isn't.' But studies are ongoing, and we're learning more all the time."

He adds that the response to different vaccines can vary depending on the formulation.

"We're coming up with some answers, and also coming up with questions that will lead to answers," says Townsend. "We shouldn't be surprised that it's complicated. When you actually sit down and think about manipulating an immune system that's been developing for millions of years, it's really arrogant!"

He cites the example of the respiratory form of EHV (equine herpesvirus, also called rhinopneumonitis or rhino). No published data shows that EHV vaccines really work, and a recent study showed poor antibody responses to a number of killed EHV vaccines on the North American market. (More information:

"We've been working on EHV since the 1930s, and we still don't know what's really going on," he says. "Yet in the case of influenza, we know quite a lot.

"We're becoming increasingly critical in the way we assess vaccines and more realistic in our expectations in terms of safety and efficacy," he adds. "When a new vaccine comes out, we're stopping to question what the best way to use it is--and that's good. A lot of people have had a check-box approach to vaccinating, and we need to come to grips with the fact that it's not nearly as simple as that."

Editor's note: Look for a 12-part series of articles on vaccination coming in 2005.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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