Age-specific Risk of Herpes Zoster in Immunocompetent Adults ≥18 Years-of-age—A Retrospective Cohort Study in the United States

Background: Approximately one-third of United States (US) individuals develop herpes zoster (HZ). Recent HZ incidence data are lacking, especially in immunocompetent adults 18-49 years-of-age (YoA). Recombinant HZ vaccine is recommended for US adults ≥50 YoA and immunocompromised/immunosuppressed adults ≥19 YoA. Methods: This retrospective cohort study (2015-2022, Merative MarketScan Commercial/Medicare) estimated age-specific HZ burden and incidence rates (IRs) per 1000 person-years in immunocompetent adults (≥18 YoA), and calculated HZ adjusted IR ratios (aIRRs) versus 50-59 YoA. Using the predetermined noninferiority margin of 0.62, HZ aIRRs versus 50-59 YoA were significantly higher (95% confidence interval lower limit [95% CI LL] > 1.0), comparable (95% CI LL >0.62 and ≤1.0), or inconclusive (other result). HZ definition: International Classification of Diseases (ICD-10) code B02.2x plus antiviral within 7 days (only ICD-10 in sensitivity analysis). Immunocompetent definition: no comorbidities (ie, asthma, chronic kidney disease, chronic obstructive pulmonary disease, diabetes, depression, stress, and trauma) or immunocompromising/autoimmune disease or medication. Results: In this immunocompetent population without comorbid conditions (57% of adults overall), HZ IR increased with age, from 0.77 (18-29 YoA) to 4.67 (≥80 YoA). HZ risk was comparable in 30-39 YoA (aIRR 0.66 [95% CI 0.64-0.68]) and 40-49 YoA (0.75 [0.73-0.77]) versus 50-59 YoA. Proportions with postherpetic neuralgia (from 40 to 49 YoA) and HZ hospitalization (from 60 to 69 YoA) tended to increase with age. In sensitivity analyses using a broader HZ definition, HZ burden was ∼30% higher. Conclusions: The study identified a substantial HZ burden in younger immunocompetent adults (30-49 YoA) without comorbid conditions, with statistically comparable IRs versus 50-59 YoA.