OBJECTIVES: Older adults are often evaluated as one homogeneous group. As currently illustrated with the COVID-19 pandemic, older adults are however heterogeneous in risk factors for infection and disease, including, for example, frailty, immunity, and clustering. This research aims to assess the use and the importance of including such heterogeneity in older adults in health economic evaluations of preventive interventions, such as vaccinations.

METHODS: Multiple scoping reviews were conducted to identify the internal (e.g. immunosenescence, comorbidity, and lifestyle) and external (e.g. social interaction, and location such as nursing homes) risk factors in older adults for acquiring infectious diseases and their related consequences. Both, inclusion and presence of risk factors were assessed, derived from economic evaluations and observational studies. We determined which older adults are more vulnerable to respiratory infections (and related disease), such as influenza, pneumococcal and respiratory syncytial virus (RSV) infections. We evaluated the critical heterogenic characteristics that should be considered in the assessment.

RESULTS: Scientific literature typically underreports the broad ranges of heterogeneity in older adults that impact on the risk of acquiring infectious diseases and related disease in the economic assessments of preventative strategies. Only a few publications are available that incorporate crucial internal and/or external factors, such as frailty and location. The impacts of the heterogeneity in these risk factors are not precisely measured beyond age. Yet, immunosenescence, levels of frailty, and comorbidities, such as diabetes and obesity are considered crucial internal heterogeneity factors. The interplay between location/clustering and exact timing (seasonality in epidemics) should be considered core external triggers in heterogeneity, potentially impacting the cost-effectiveness.

CONCLUSIONS: Risk factors involving heterogeneity in older adults are only sparsely incorporated in health economic evaluations of preventative interventions. Economic evaluations would benefit greatly from the inclusion of these risk factors; this would provide more precise, realistic, and robust analyses.