This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax firstname.lastname@example.org with numerous contributions by others.
Following chickenpox infection, the varicella zoster virus persists in
a latent form in sensory nerve ganglia without any signs of
illness. The virus can be reactivated causing herpes zoster or
shingles, which is a painful small blister-like rash in the
distribution of one or more sensory nerve roots. It is estimated that
15% of the population will experience zoster during their lifetimes.
Zoster develops most frequently among the elderly and among
individuals who are immunocompromised. Most people only have one
episode of herpes zoster; fewer than 4% will have repeated
episodes. Postherpetic neuralgia is a common complication; this
complication is more common among the elderly (25-50% of those over 50
who have shingles, but only 10% of all people who have shingles.
(Information on the effect of the vaccine on herpes zoster will be
added to this FAQ later.)