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 ≥50YoA and immunocompromised/immunosuppressed adults ≥19YoA. Methods This retrospective cohort study (2015–2022, Merative MarketScan Commercial/Medicare) estimated age-specific HZ burden and incidence rates (IR) per 1000 person-years in immunocompetent adults (≥18YoA), and calculated HZ adjusted IR ratios (aIRRs) versus 50–59YoA. Using the pre-determined non-inferiority margin of 0.62, HZ aIRRs versus 50–59YoA 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 (i.e., asthma, chronic kidney disease, chronic obstructive pulmonary disease, diabetes, depression, stress, 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 (18–29YoA) to 4.67 (≥80YoA). HZ risk was comparable in 30–39YoA (aIRR 0.66 [95%CI 0.64–0.68]) and 40–49YoA (0.75 [0.73–0.77]) vs. 50–59YoA. Proportions with postherpetic neuralgia (from 40–49YoA) and HZ hospitalization (from 60–69YoA) tended to increase with age. In sensitivity analyses using a broader HZ definition, HZ burden was approximately 30% higher. Conclusions The study identified a substantial HZ burden in younger immunocompetent adults (30–49YoA) without comorbid conditions, with statistically comparable IRs versus 50–59YoA.