Equine Vaccines
What Kind and How and When to Use Them

When I went equine vaccine shopping this year, I found there were two choices that allowed me to combine West Nile Virus with the usual WEE, EEE and Tetanus booster.

Ready-to-Use in preloaded syringe (RTU)
and
Vaccines Requiring Reconstitution (VRR)

(Note that these acronyms just make things easier to talk about.)

Both RTUs and VRRs are given intramuscularly (IM) using the provided syringe and 1 ½” long 20 gauge needle.

Ready-to-Use (RTU)

Vaccines that are ready-to-use, requiring no reconstitution, come as a preloaded syringe with a rubber plug and a separate needle that you attach to the syringe prior to administering. This is a relatively newer, user-friendly type of vaccine that has been available to horse owners for about 10 years.

This year RTUs are available in several combinations such as:

• West Nile + Eastern and Western Equine Encephalomyelitis (EEE and WEE)
• West Nile + Eastern, Western, and Venezuelan Encephalomyelitis
• West Nile + Eastern, Western, and Venezuelan Encephalomyelitis + Tetanus

Vaccines Requiring Reconstitution (VRR)

Vaccines that need to be reconstituted are nothing new. In fact, this was about the only way to purchase equine vaccines prior to the advent of the RTU type described above.

VRRs are comprised of a 3 part kit: one glass bottle of dried vaccine powder (in this case West Nile Virus Live Canarypox Vector), one bottle of liquid diluent (in this case Killed WEE, EEE and Tetanus diluent), and one syringe with needle.

Using the syringe and needle, the diluent is drawn out of the bottle and injected into the bottle containing the dried vaccine. The mixture is shaken until thoroughly mixed. The mixture is drawn out of the bottle with the needle and administered to the horse.

Advantages - Disadvantages - Potential Problems

VRRs use a fairly foolproof procedure but the vet tech that sold the vaccines said that the following problems could occur so she reminds people to:

1. Don’t forget to add the diluent to the dry mixture. (She said horseowners administer the diluent only, then call and ask how they can give the dry portion after the fact ? you can’t !!)
   
   
2. Mix thoroughly - if there is inadequate mixing, particles could clog the needle or the product won’t dissipate correctly in the horse's tissues.
   
   
3. Administer within 20 minutes of reconstitution or risk less efficacy.
   
   
4. Be sure to use the correct diluent. If you have more pharmaceuticals in your barn refrigerator, be sure you don’t grab the epinephrine or something else by mistake !

Which One?

Because the vaccines requiring reconstitution were $3 per head less expensive and because I am familiar with using that method, I purchased the vaccines requiring reconstitution. If you have a large number of horses, consider RTU to save time, and consider VRR to save money. Both types are available in single dose and multiple dose vials. Multiple dose vials are always less expensive per head. As always, confer with your veterinarian.

One or Two West Nile Inoculations?

Although WEE, EEE and Tetanus boosters are given once a year, it is often suggested that in areas with early and long mosquito seasons or a high incidence of West Nile Virus, a booster should be given 3-4 months after the first vaccination in the spring.

For the RTU vaccine, it was suggested I purchase two for each horse, one to use early in the mosquito season and one later in the summer or early fall as a booster.

For the VRR, it was not suggested that I purchase two for each horse - one inoculation is supposed to keep the horse’s titer up high enough during the entire mosquito season. The technology behind that vaccine product is supposed to produce a stronger and longer lasting reaction in the horse.

Note: here at 7000 feet in semi-arid Colorado, we don’t see mosquitoes until late in the summer if at all, so I vaccinate in May or June and that is thought to be sufficient to protect them through the end of mosquito season. If you are in other locations, you might vaccinate in March and again in summer or early fall. Confer with your veterinarian.