[Road to Island Reds]

I am fairly new to the keeping chickens, i was given 10 chickens 18 months ago and have fairly good success with eggs but recently i have had three die over a period of 6 months, i have taken them down the vet and they have died through a viral infection which attacks the nervous system to a point where they cant stand up and they go off there feed and water, i wasnt told if the birds had any vaccinations when they were young, is there any vaccination they should have or should of had, i think the birds are about 8 years old now
They reside in a stable which they have straw bedding, bales of straw to perch on and nesting boxes

[bantam novice]

Hello and welcome to the forum.   
This sounds as if it could be Mareks disease and if that is the case there is no vaccination that you can give them now.  Chicks should be vaccinated at day old but as the vaccination is sold in very large batches, is expensive and will only be viable for a short time after it has defrosted many small scale poultry breeders don't bother.  If you google Mareks disease there should be some information for you.  Did the vet mention Marek's disease?

[Sassy]

At 8 years old they could just be more susceptible to anything going around. They are a very respectable age. 

[Road to Island Reds]

The vet had not come across it before he could only tell the infected chicken(s) wernt very well and they would not survive long and that he would have to send it away for analysis, i shall start again with a new flock in the spring