Has the Childhood Varicella Vaccine Increased Herpes Zoster Incidence in the Unvaccinated Elderly?

Herpes zoster (HZ) is a painful dermatomal vesicular eruption that may lead to prolonged postherpetic neuralgia. The condition results from the reactivation of varicella-zoster virus that has been latent in dorsal root ganglia since the affected person had chickenpox. Vaccination against varicella, routine since 1996, has very successfully reduced the incidence of natural varicella infection.

To determine whether lack of exposure to natural infection, which theoretically would boost immunity, might lead to increased HZ incidence in the unvaccinated elderly population, investigators retrospectively analyzed the incidence of HZ in a random 5% sample of Medicare recipients (2,845,353 people older than age 65) from 1992 to 2010. They used a Medi…