Frail elderly individuals are more likely to have poor clinical outcomes. As a result, frailty evaluation is critical in clinical trials to identify the advantages and drawbacks of treatments. However, there is no agreement on how frailty should be measured. Within an adjuvanted recombinant zoster vaccine (RZV) study, researchers created a prospectively specified index utilizing a battery of formal tests and tools, as well as a retrospectively constructed index using medical comorbidities and patient reported outcomes (PROs). A total deficit score was computed as the accumulation of deficits for both frailty indices (FIs), and subjects were classified as non-frail, pre-frail, or frail. They looked at (1) the feasibility and validity of both FIs, as well as (2) the effect of RZV vaccination reactogenicity by frailty state on Short Form-36 physical functioning (PF) scores. Using the prospective FI, 236 of 401 individuals aged 50 years were classified as non-frail, 143 as pre-frail, and 22 as frail. For the retroactive FI, the corresponding figures were 192, 169, and 40, respectively. There was a high degree of agreement across the frailty status evaluations. For the prospective FI, the proportion of frail participants rose from 1.5 percent to 10.4 percent in individuals aged 50–59 and 70 years, respectively. In frail individuals, RZV vaccination was linked with a temporary, non-clinically significant reduction in the SF-36 PF score.

Both frailty indexes produced comparable findings. The FI developed retrospectively has the benefit of being simpler to include into vaccination clinical studies for older individuals.