Differentiating Mpox Infection and Vaccination Using a Validated Multiplex Orthopoxvirus IgG Serology Assay

Area of Science:

• Virology
• Immunology
• Clinical Diagnostics

Background:

• Monkeypox virus (MPXV) outbreaks necessitate reliable serological assays for exposure and immunity assessment.
• Orthopoxvirus cross-reactivity complicates differentiating antibody responses between natural MPXV infection and vaccination/other exposures.

Purpose of the Study:

• To validate the Meso Scale Discovery (MSD) V-PLEX Orthopoxvirus Panel 1 (IgG) Kit for quantifying antibody levels against MPXV and vaccinia virus (VACV) antigens.
• To assess the assay's performance in distinguishing between MPXV infection and JYNNEOS vaccination using clinical samples.
• To evaluate the utility of ortholog pair ratio analysis for differentiating exposure types.

Main Methods:

• Assay validation following Good Clinical Laboratory Practice (GCLP) guidelines.
• Testing serum samples from individuals with prior mpox, JYNNEOS vaccine recipients, and unexposed controls.
• Receiver operating characteristic (ROC) analysis to determine sensitivity and specificity for exposure detection and differentiation.

Main Results:

• The MSD assay reliably detected antibody responses in all exposed cohorts, with peak levels at 2 months post-vaccination.
• Individual antigens showed high sensitivity for exposure detection, but poor performance in distinguishing infection from vaccination.
• Ortholog pair ratio analysis, specifically MPXV A35R/VACV A33R, effectively differentiated MPXV infection from vaccinia vaccination (AUC = 0.97).

Conclusions:

• The MSD V-PLEX Orthopoxvirus Panel 1 (IgG) Kit is validated for clinical research and serosurveillance of MPXV immunity.
• Ortholog pair ratio analysis is a valuable strategy for discriminating between MPXV infection and vaccinia virus vaccination.
• This approach enhances the accuracy of serological assessments in the context of orthopoxvirus exposures.