Every year, the shingles virus affects an estimated 1 million people in the United States. It is a painful, unpleasant (though rarely fatal) illness which is a reactivation of the chickenpox virus you had as a child. As your immune system weakens with age, the virus reactivates from where it has been lying dormant in your spinal column. It causes blisters and pain along whole nerve segments in your body. The blisters may come and go after a couple weeks, but the pain can persist for months.