West Nile

We lost a horse last night to west nile.  She was a rescue horse that had been taken from someone else because of neglect.  Our other horses have been vaccinated for west nile...she was to be, but died from that very thing before the vet got to us to do it.  My question is, how long is the west nile vaccine good for? How often do we need to do this?  We have recently bought another pony for my son and he's not been vaccinated for it, so we have already called and since we've already lost one to it, the vet is coming up ASAP to get him.  I could wait and ask him, but was just curious about it and thought someone here might be able to answer.  Thanks.

[Davidsbabygirl]

the west nile vaccination is given in two doses if the horse has never been vaccinated before.  The first one takes action fast and holds until the second dose is given two weeks later, but full immunity is not provided until the second injection is given.  After the initial doses, it is recommended that the horse be vaccinated annually for WNV.  Other options in the mean time include fly masks and sheets, mosquito repellents for horses, keeping the horses indoors, limiting standing water, and other various options.  I hope things work out and if you need help with anything horsey, I am a horse trainer of 17 years and always looking for horsey friends.  I can be reached on yahoo under the name solsticeparadox.  Thanks!