BACKGROUND: Burden of vaccine-preventable diseases in the United States (US) remains high among older adults, despite longstanding immunization recommendations. Accelerated population aging may add to the already significant disease burden in the absence of increased vaccination rates. This study aimed to quantify the impact of aging on future burden of influenza, herpes zoster (HZ), and pertussis in US adults aged 50+ years.
METHODS: A population-based, age-structured economic model was developed to project burden of influenza, HZ, and pertussis using disease-specific decision trees that account for case severity and resource use. The model started with the 2017 US adult population aged 50+ years stratified by 1-year age groups. In each subsequent year, corresponding US Census Bureau population projections were used to calculate undiscounted cases and direct medical costs (2017 US$), keeping current estimates of age-specific disease incidence, vaccine coverage, and efficacy constant over time. Results were calculated over multiple time horizons and for multiple diseases and scenario analyses were conducted.
RESULTS: In 2017, influenza burden was estimated at ~7.57 million cases, with corresponding direct medical costs of $6.6 billion. Over a 10-year horizon, the model projected an additional ~4.98 million cumulative influenza cases solely due to population aging, with nearly $7.0 billion in additional costs. In each year, most costs were attributed to adults aged 65+ years (range: 67.5-74.2%) and unvaccinated individuals (range: 53.7-55.0%). Excess cases and costs due to population aging were further augmented when projecting over longer time periods. Results for HZ and pertussis also showed increases in disease burden due to population aging.
CONCLUSION: Holding current incidence and vaccination levels constant over the next decade, the model projects notable increases in influenza, HZ, and pertussis burden due to population aging, with a corresponding impact on healthcare resource use and medical costs. Efforts to further increase vaccination rates in older adults are warranted.
DISCLOSURE: GlaxoSmithKline Biologicals SA funded this study (GSK study identifier: HO-17-18466) and all costs related to the development of all related publications.
