Comparison of the Levels of Immunogenicity and Safety of Zostavax in Adults 50 to 59 Years Old and in Adults 60 Years Old or Older

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Abstract
Zostavax has been shown to be efficacious in the prevention of herpes zoster and generally well tolerated in clinical trials among subjects 60 years old or older. This prespecified combined analysis from two studies compares the levels of immunogenicity and safety of Zostavax in subjects 50 to 59 years old versus those in subjects >or=60 years old. Varicella-zoster virus (VZV) antibody (Ab) titers were measured by glycoprotein enzyme-linked immunosorbent assay at baseline and 4 weeks postvaccination. Noninferiority was evaluated by estimated geometric mean severalfold rise (GMFR) ratio (50 to 59 years old/>or=60 years old) and two-sided 95% confidence interval (CI). Success was defined by a lower bound (LB) of the 95% CI of the GMFR ratio of >0.67. Acceptability of postvaccination VZV Ab was defined by an LB of the 95% CI of the GMFR of >1.4. Safety data were recorded for 28 days postvaccination by standardized vaccination report card. The estimated GMFRs from baseline to 4 weeks postvaccination were 2.6 (95% CI, 2.4, 2.9) in subjects 50 to 59 years old and 2.3 (95% CI, 2.1, 2.4) in subjects >or=60 years old. The estimated GMFR ratio (50 to 59 years old/>or=60 years old) was 1.13 (95% CI, 1.02, 1.25). No serious Zostavax-related adverse experiences were reported. After a dose of Zostavax, the GMFR of the VZV Ab response in subjects 50 to 59 years old was noninferior to that in subjects >or=60 years old. The VZV Ab response was acceptable in both age groups. Zostavax was generally well tolerated in both age groups.