Table 1.

Outline of the 3 methods.

Method 1: Youden Index (YI) Threshold Method • Requires overlap of distributions of baseline and postvaccination values • May not be able to efficiently differentiate between vaccine doses if baseline levels are low and/or have small overlap with postvaccination levels • Apply a single YI threshold value for each assay that best discriminates between overall baseline and postvaccination biomarker levels • For each dose formulation and all doses combined, calculate percentage of subjects with postvaccination values greater than or equal to the YI threshold for each assay individually or simultaneously for assay combinations Method 2: ROC Relative to Baseline (ROC-B) Method • Uses the distribution of all baseline values as a reference • Requires overlap of distributions of baseline and postvaccination values • May not be able to efficiently differentiate between vaccine doses if baseline levels are low and/or have small overlap with postvaccination levels • For each dose formulation and all doses combined, construct ROC curve and surface using threshold values from the full range of baseline levels • Calculate AUC of ROC curve for individual assay and VUS of ROC surface for assay combinations • AUC and VUS values measure degree of separation of postvaccination values of individual formulations from the distribution of overall baseline values Method 3: ROC of Postdose (ROC-P) Level Method • The ROC-P method uses postvaccination data only and can be applied to situations when the YI and ROC-B methods are not suitable • Applies to both seropositive and seronegative populations • Uses the pooled postvaccination values as a reference distribution • For each dose formulation and all doses combined, construct ROC curve and surface using threshold values from the full range of postdose levels • Calculate AUC of ROC curve for individual assay and VUS of ROC surface for assay combinations • AUC and VUS values measure degree of separation of postdose values of individual formulations from the distribution of pooled postvaccination values Dose selection approach: Each of the 3 methods evaluates and visualizes the immunogenicity of different formulations by comparing each formulation to the overall dose effect of all formulations combined and selecting the formulation with the highest and most robust immune responses.

AUC, area under the curve; ROC, receiver-operating characteristic; VUS, volume under the surface.