Herpes Zoster and Postherpetic Neuralgia: a review of the effects of vaccination.

Herpes zoster (HZ) results from reactivation of varicella zoster virus which has been persistent but clinically latent in dorsal root and cranial nerve ganglia since primary infection, usually as a child, with varicella (chicken pox). HZ affects 20-30% of individuals during their lifetime and up to 50% of those > or =80 years old. Although serious life- or sight-threatening complications occur rarely, postherpetic neuralgia (PHN) is the most common complication. Both HZ and PHN are most common in the elderly. Declining cell-mediated immunity resulting from immune senescence appears to be the cause. Incidence of HZ is also high in individuals who are immunocompromised as a result of disease or its treatment. HZ also occurs in younger and fit individuals but is usually mild and complications are rare. Current management of HZ with antiviral drugs and analgesics attains quite good control of acute pain and skin rash but offers only partial protection against PHN. Other strategies studied to prevent PHN such as nerve blocks are relatively ineffective and clinically impractical. Although several drug classes are used to manage PHN, numbers needed to treat to obtain 50% pain reduction range from approx. 2.5-5 and adverse effects are common. The elderly population is growing and thus the number of HZ and PHN susceptible individuals is increasing. HZ and PHN are expensive in terms of suffering, loss of independence and healthcare costs. Significant numbers of the elderly with HZ require hospitalization. Short-term illness in the elderly can lead to long-term loss of independence. A live attenuated herpes zoster vaccine has been studied in a large number of subjects and shown to reduce incidence of HZ as well as incidence and severity of PHN. The safety profile of the vaccine is good, local soreness at the injection site being the only common adverse event. Health economics studies suggest that vaccination of adults about 60 years of age would be cost effective. Duration of protection following vaccination is the subject of ongoing surveillance, as is the potential benefit of vaccinating younger and sicker members of the population.