Preventing Shingles

Shingles, also known as Herpes Zoster, usually occurs in elderly adults. It is characterized by painful eruption of vesicular lesions that follow a dermatomal distribution. The thoracic and lumbar roots are most commonly affected.

Pain precedes the appearance of the lesions and is severe and debilitating. The incidence and severity of herpes zoster increases with increasing age due to age related decline in immunity. Post herpetic neuralgia is a common complication of herpes zoster in the elderly. Facial nerve paralysis, herpes zoster ophthalmicus and bacterial superinfection are among other complications. Antiviral therapy with Acyclovir reduces the duration of the illness. A live attenuated Varicella Zoster Virus vaccine is also available to prevent herpes zoster.

Herpes zoster in the neck. Image from wikipedia.

In a recent study published in JAMA, Hung Fu Tseng et al. examined the effect of a Oka/Merck strain of varicella zoster virus based vaccine in reducing the incidence of herpes zoster. The study was a retrospective cohort study conducted among members of Kaiser Permanente, Southern California. The study included 75761 vaccinated subjects in 60 years or more age group. 227283 unvaccinated subjects in 60 years of more age group were included as controls. The controls were randomly selected and age matched. Immunocompromised individuals were excluded from the study as the vaccine is contraindicated in them. Exclusion of immunocompromised subjects also removes its confounding effect as it is a risk factor for herpes zoster. The main outcome of interest was incidence of herpes zoster. Bias was accessed by measuring the rate ratios of 13 different acute conditions which are not protected by the vaccine. If the rate ratios of these conditions are not grouped around 1, it would indicate that the vaccinated and the unvaccinated groups differ from each other and unmeasured confounders are at play. The rate ratio of herpes zoster was much greater in magnitude than the other conditions indicating that the outcome was not due to any bias.

In univariate analysis, the incidence of herpes zoster in vaccinated individuals was 6.4 (95% CI, 5.9-6.8) per 1000 person-years and among unvaccinated individuals, it was 13.0 (95% CI, 12.6-13.3) per 1000 person-years. The risk of herpes zoster among unvaccinated individuals varied with age, sex, race and lung disease. The difference in incidence of herpes zoster persisted upon adjustment for sex, race, chronic diseases and health care utilization. The fully adjusted analysis gave a hazard ratio of 0.45 (95% CI, 0.42-0.48). When a more strict criteria for immunocompetency was used, the adjusted hazard ratio was 0.46 (95%CI, 0.43-0.49). The vaccine also reduced the risk of herpes zoster ophthalmicus and hospitalization due to herpes zoster. Overall reduction in incidence of herpes zoster was 55%.

The limitations of the study are potentially unmeasured confounders and external validity.

Reference:

Tseng HF, Smith N, Harpaz R, Bialek SR, Sy LS, & Jacobsen SJ (2011). Herpes zoster vaccine in older adults and the risk of subsequent herpes zoster disease. JAMA : the journal of the American Medical Association, 305 (2), 160-6 PMID: 21224457