OBJECTIVES: To characterize trends in recombinant zoster vaccine (RZV) initiation and examine their association with potential prognostic factors.

METHODS: From a large, national insurer, we identified individuals 51 years or older in 2017 who were continuously enrolled from August 1, 2016 to October 23, 2017, and not missing sociodemographic variables. Individuals were followed from October 23, 2017 through the earliest of disenrollment, death, RZV initiation, or December 31, 2021. RZV initiation was defined as completing the first dose of RZV. Patient demographics and potential prognostic factors included age in 2017, sex, race/ethnicity, Charlson Comorbidity Index (CCI) score, herpes zoster (HZ) in the past 12 months, and influenza vaccination status during the 2016-17 influenza season. Cumulative incidence function curves and the Gray’s test assessed the unadjusted difference in RZV initiation by each factor. A competing-risk analysis examined the association of RZV initiation with potential prognostic factors, with RZV initiation, death, and disenrollment/end of follow-up period as the event of interest, the competing event, and the censoring event, respectively.

RESULTS: A total of 5,104,523 enrollees were identified from the database. With a median follow-up of 1,149 days, 758,775 (14.9%) enrollees received a first dose of RZV and 570,138 (11.2%) died. The 1-, 2-, 3-, and 4-year RZV initiation rates were 3.0%, 7.5%, and 11.5% and 14.9%, respectively. RZV initiation was significantly differentiated by all factors on a univariate basis (p<0.001). After adjusting for all other factors, the competing-risk analysis showed that age, sex, race/ethnicity, CCI, HZ history, and influenza vaccination were all significant prognostic factors for RZV initiation (p<0.001). Aged over 65 years old, being Hispanic or non-Hispanic black, and having higher CCI score were negatively associated with RZV initiation.

CONCLUSIONS: RZV initiation rates were suboptimal. More research and public health efforts are needed to understand and address the low RZV initiation.