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Zostavax: A New Vaccine to Reduce the Risk for Herpes Zoster in Older Adults

Results from a large study show this new vaccine to be very effective, particularly in 60- to 69-year-olds.

Background:
Herpes zoster (HZ), or shingles, is caused by the reactivation of latent varicella-zoster virus (VZV) years after an initial varicella infection. About one million cases occur in the U.S. each year, most of them in individuals older than 60. The acute episode of unilateral vesicular eruption is often associated with severe pain; a debilitating, age-related, treatment-refractory complication, postherpetic neuralgia (PHN), can last for months. Although prompt treatment with antiviral drugs such as famciclovir shortens the duration of the initial rash and pain, these agents do not prevent PHN. Waning cell-mediated immunity to VZV is thought to underlie HZ’s age-related incidence and severity, and the new vaccine appears to work by boosting this immunity. Zostavax was licensed by the FDA on May 25, 2006.

Vaccine Composition:
Zostavax is a lyophilized preparation of the Oka/Merck strain of live attenuated VZV. Each 0.65-mL dose contains 19,400 plaque-forming units, compared with 1350 PFU in the VZV vaccine used for primary immunization of children. The vaccine has no preservatives and must be stored frozen until <30 minutes before use.

Target Population and Immunization Schedule:
The vaccine is indicated for people aged 60. It is contraindicated in individuals who are immunocompromised for any reason, including use of high-dose corticosteroids. Other contraindications include severe allergy to any vaccine components, active tuberculosis, and pregnancy. The vaccine is administered as a single dose, injected subcutaneously.

Effectiveness:
In the Shingles Prevention Study, a randomized, double-blind, prospective, partially industry-sponsored trial, Veterans Affairs researchers compared Zostavax with placebo in 38,546 individuals aged 60. Randomization was stratified by age (60–69 years old and 70 years old). Median follow-up time was 3.1 years (range, 1 day to 4.9 years). HZ incidence was reduced by 51% in vaccine recipients overall; efficacy was highest (64%) in subjects 60–69 years old and decreased with age. Among subjects who developed HZ postvaccination, the duration and severity of pain and discomfort were significantly less in vaccine than in placebo recipients. PHN (defined as moderate to severe pain persisting or appearing >90 days after the onset of HZ rash) was decreased by 39% overall in vaccine recipients who developed HZ postvaccination, but the greatest effect on decreasing PHN was due to preventing HZ in the first place.

Adverse Effects:
Serious adverse events occurred at a similar rate (1.4%) in vaccine and placebo recipients. Vaccine-related serious events, including asthma exacerbation and polymyalgia rheumatica, occurred in two vaccine recipients and three placebo recipients. Local reactions at the injection site were more common in vaccine recipients. Vaccine virus was not detected in lesions of vaccine recipients who developed zoster, and the researchers saw no evidence that the vaccine virus spread to others.

Comment: HZ and subsequent PHN can be seriously debilitating, and Zostavax appears to be very effective in preventing HZ in adults who have not previously had this condition. Although protection against PHN is not an approved indication for vaccination, the incidence of this complication also was significantly reduced in vaccine recipients. Long-term protection, the need for additional boosting doses, and the occurrence of postmarketing adverse events await further study.

— Stephen G. Baum, MD

Published in Journal Watch Infectious Diseases June 22, 2006

Citation(s):

Zostavax package insert . May 2006. (http://www.fda.gov/cber/label/zosmer052506LB.pdf)

US Food and Drug Administration. FDA News: FDA licenses new vaccine to reduce older Americans’ risk of shingles. Accessed at http://www.fda.gov/bbs/topics/NEWS/2006/NEW01378.html on May 26 , 2006.

Oxman MN et al. A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults. N Engl J Med 2005 Jun 2; 352:2271-84.

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