Immunogenicity and safety of ZOSTAVAX(®) approaching expiry potency in individuals aged ≥50 years.

ABSTRACT

BACKGROUND: Age is a major risk factor for herpes zoster (HZ) and its potential long-term complication post-herpetic neuralgia (PHN). Due to the significant burden of HZ and PHN on patients' quality of life, it is vital that effective and well-tolerated vaccines are available to prevent HZ in older adults. ZOSTAVAX(®) vaccine was developed to prevent HZ and PHN in individuals ≥50 years (y) of age, and its clinical efficacy and safety have been demonstrated. AIMS AND METHODS: This phase 4, open-label, multicenter study was undertaken to assess the immunogenicity and safety of a single dose of ZOSTAVAX (refrigerator-stable formulation) given within 6 mo of its expiry date in individuals ≥50 y of age. The geometric mean fold rise (GMFR) from pre-vaccination to 4 weeks post-vaccination in varicella zoster virus (VZV) antibody titers was calculated. An acceptable antibody response was defined as a lower 95% confidence interval (CI) of GMFR > 1.4. Solicited and unsolicited injection-site reactions and systemic adverse events were recorded. RESULTS: The GMFR in VZV antibody titers was 3.1 (95% CI 2.6, 3.8), satisfying the criterion for an acceptable VZV antibody response to ZOSTAVAX (minimum requirement 1.4 GMFR). An acceptable rise in VZV antibody titers was observed in individuals of 50-59 y of age (GMFR 3.9; 95% CI 2.9, 5.1) and in those ≥60 y of age (GMFR 2.5; 95% CI 1.9, 3.2). ZOSTAVAX was well tolerated; no serious adverse events were reported. CONCLUSION: ZOSTAVAX elicits an acceptable immune response in immunocompetent individuals ≥50 y of age when stored as directed and administered during the 6 mo prior to expiration.