Development of a novel serology assay for the detection of IgG antibodies to identify exposures to orthopoxviruses

Abstract The World Health Organization has declared a Public Health Emergency for an ongoing mpox (formerly monkeypox) outbreak, due to multiple cases of mpox in regions of the world in which infections have not been previously seen. The outbreak is notable for the high degree of human-human transmissions spreading primarily through sexual contacts. Currently, as a prophylactic (and post-exposure) measure, high-risk individuals are being offered immunization with cross-reactive vaccinia virus (VV) vaccines, a strategy previously used for the closely related variola (smallpox) virus. Commercial tests to measure binding antibodies to mpox for diagnostics or surveillance are not (yet) available. We present here a novel IgG detection assay to identify or measure binding antibodies to mpox and VV. This multiplexed, Luminex-based serology assay contains multiple recombinant proteins or peptides derived from VV and mpox. Because the assay contains antigens present on orthopoxviruses including VV, but also contain antigens present on orthopoxviruses exceptVV, the test allows for serological distinction between infection with virulent orthopoxviruses and attenuated strains of VV. We present data on detection of antibodies elicited by childhood (smallpox) or recent (mpox) vaccination, mpox infection, and breakthrough infection in previously vaccinated individuals. We demonstrate that the baseline antibody profiles of high-risk populations are distinct and must be considered when assessing mpox serology information. Overall, these data support the use of Luminex-based serology as a diagnostic tool for mpox infections and as a surveillance tool to detect the prevalence of mpox infections, even within a vaccinated population. This work was supported by Cooperative Agreement Number NU50CK000516 funded by the Centers for Disease Control and Prevention. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention or the Department of Health and Human Services.