Real-world evidence on adherence and completion of the two-dose recombinant zoster vaccine and associated factors in U.S. adults, 2017–2021

Introduction: Poor compliance with adult vaccination recommendations contributes to substantial disease burden. Evidence on adherence, completion, and completion timeliness for the 2-dose recombinant herpes zoster vaccine (RZV) and factors associated with these outcomes is limited and not readily generalizable for the entire U.S. Methods: This retrospective, observational study examined adherence, completion, and the impact of sociodemographic, clinical and geographical factors among U.S. adults ≥ 50 years receiving RZV (4/20/2017 to 3/31/2021), using a large, geographically representative administrative claims database. Continuous enrollment in a medical benefit plan for six months prior to and following the index date (first observed vaccine dose) was required. Adherence was defined as receipt of the 2nd dose within 2–6 months, per label recommendation. Completion (receipt of all doses) was assessed at 6, 12, 18, and 24 months. Results: Among 726,352 adults included, the adherence rate was 71.8%. Among 208,311 adults with 24–month follow-up, the completion rate was 72.3% after 6 months and 86.2% after 24 months. Logistic regression showed low adherence/completion was associated with younger age, Black or Hispanic race/ethnicity, lower income, lower educational attainment, and possessing commercial rather than Medicare healthcare insurance. Recipients identified using pharmacy claims had much higher adherence (74.0%) than those identified using medical claims (48.0%). Conclusions: Adherence and completion rates for RZV are suboptimal, especially for adults aged 50–64, racial/ethnic minorities, individuals with lower socio-economic status and those without Medicare insurance. More research and public health efforts are needed to understand and address potential barriers to RZV uptake, adherence and completion.