Cost-effectiveness of routine catch-up hepatitis a vaccination in the United States: Dynamic transmission modeling study.

BACKGROUND: Despite routine vaccination of children against hepatitis A (HepA), a large segment of the United States population remains unvaccinated, imposing a risk of hepatitis A virus (HAV) to adolescents and adults. In July of 2020, the Advisory Committee on Immunization Practices recommended that all children and adolescents aged 2-18 years who have not previously received a HepA vaccine be vaccinated. We evaluated the public health impact and cost-effectiveness of this HepA catch-up vaccination strategy. METHODS: We used a dynamic transmission model to compare adding a HepA catch-up vaccination of persons age 2-18 years to a routine vaccination of children 12-23 months of age with routine vaccination only in the United States. The model included various health compartments: maternal antibodies, susceptible, exposed, asymptomatic infectious, symptomatic infectious (outpatient, hospitalized, liver transplant, post- liver transplant, death), recovered, and vaccinated with and without immunity. Using a 3% annual discount rate, we estimated the incremental cost per quality-adjusted life year (QALY) gained from a societal perspective over a 100-year time horizon. All costs were converted into 2020 US dollars. FINDINGS: Compared with the routine vaccination policy at 12-23 months of age over 100 years, the catch-up program for unvaccinated children and adolescents aged 2-18 years, prevented 70,072 additional symptomatic infections, 51,391 outpatient visits, 16,575 hospitalizations, and 413 deaths. The catch-up vaccination strategy was cost-saving when compared with the routine vaccination strategy. In scenario analysis allowing administering a second dose to partially vaccinated children, the cost-effectiveness of was not favorable at a higher vaccination coverage ($196,701/QALY at 5% and $476,241/QALY at 50%). INTERPRETATION: HepA catch-up vaccination in the United States is expected to reduce HepA morbidity and mortality and save cost. The catch-up program would be optimized when focusing on unvaccinated children and adolescents and maximizing their first dose coverage.

Understanding the role of exogenous boosting in modeling varicella vaccination.

INTRODUCTION: The exogenous boosting (EB) hypothesis posits that cell-mediated immunity is boosted for individuals reexposed to varicella-zoster virus (VZV). Historically, mathematical models of the impact of universal childhood varicella vaccination (UVV) have used limited data to capture EB and often conclude that UVV will temporarily increase herpes zoster (HZ) incidence. AREAS COVERED: We updated a 2013 systematic literature review of 40 studies to summarize new evidence from observational or modeling studies related to EB and its parameterization. We abstracted data on observational study designs and mathematical model structures, EB frameworks, and HZ-related parameter values. EXPERT COMMENTARY: This review identified an additional 41 studies: 22 observational and 19 modeling studies. Observational analyses generally reported pre-UVV increases in HZ incidence, making it difficult to attribute post-UVV increases to UVV versus other causes. Modeling studies considered a range of EB frameworks, from no boosting to full permanent immunity. Mathematical modeling efforts are needed in countries with long-standing vaccination programs to capture the dynamics of VZV transmission and temporal changes that may affect HZ incidence. Use of real-world pre-/postvaccination data on varicella and HZ incidence to validate model predictions may improve approaches to EB parameterization and understanding of the effects of varicella vaccination programs.