West Nile Disease Prevention in California

I am grateful to be a part of a very responsible group of horse lovers at Rose Bowl Riders.  When I heard from Ariel that the vets will be out to give West Nile Virus, and Flu/Rhino shots, I wondered how important it is to get these shots. We don't have a lot of mosquitos in California.   I found a very good video on youtube by theHorse.com:  this video shows the clinical signs:  http://www.youtube.com/watch?v=BJtVP5Bd5bs&NR=1.