In a question and answer session following her West Nile Virus presentation during the Western Veterinary Conference (held Feb. 15-19 in Las Vegas, Nevada), Eileen Ostlund, DVM, PhD, head of the equine and ovine viruses section at the Diagnostic Virology Laboratory, National Veterinary Services Laboratory in Ames, Iowa, offered the following answers to the audience’s questions.

Can you use Merial’s recombinant canarypox vaccine to booster horses after using the killed Fort Dodge vaccine?
We don’t know yet. We need to measure antibody levels before and after the booster vaccination to see if it is protective. I’d want to see the data before saying yes or no. The same proteins are targeted, but how the two different formats interact is not really known.

Does an infected, previously vaccinated horse need a booster?
If you couldn’t vaccinate all of your horses, I’d skip these. In general, vaccination won’t hurt, and it really only helps. It’s a cost-benefit issue, but I would probably just do it. We don’t really know enough to recommend not vaccinating these horses.

If you have a horse with a suspected reaction to one vaccine, would he have the same reaction to the other vaccine?
It’s hard to say–it depends on if the reaction was to the virus component, culture, adjuvant, vector, etc. Most likely, the reaction is to something other than the virus component, so it’s worth a try. Have a bottle of epinephrine on hand just in case