Vinyl is necessary if incontinence is an issue or might be an issue in the future it can be washed with 1 part bleach to 10 parts water because liquids cannot pass through the vinyl.
For those interested in vinyl, keep in mind that vinyl can be slippery for those uneasy on their feet. The liquids can seep into the side cracks of the seat cushion and still be absorbed by the foam below the vinyl.