Validation of xMAP SARS-CoV-2 Multi-Antigen IgG assay in Nigeria

by Nnaemeka C. Iriemenam, Fehintola A. Ige, Stacie M. Greby, Augustine Mpamugo, Ado G. Abubakar, Ayuba B. Dawurung, Mudiaga K. Esiekpe, Andrew N. Thomas, Mary U. Okoli, Samuel S. Awala, Blessing N. Ugboaja, Chicago C. Achugbu, Ifeanyichukwu Odoh, Felicia D. Nwatu, Temitope Olaleye, Loveth Akayi, Oluwaseun O. Akinmulero, Joseph Dattijo, Edewede Onokevbagbe, Olumide Okunoye, Nwando Mba, Ndidi P. Agala, Mabel Uwandu, Maureen Aniedobe, Kristen A. Stafford, Alash’le Abimiku, Yohhei Hamada, Mahesh Swaminathan, McPaul I. Okoye, Laura C. Steinhardt, Rosemary Audu

There is a need for reliable serological assays to determine accurate estimates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence. Most single target antigen assays have shown some limitations in Africa. To assess the performance of a multi-antigen assay, we evaluated a commercially available SARS-CoV-2 Multi-Antigen IgG assay for human coronavirus disease 2019 (COVID-19) in Nigeria.

Validation of the xMAP SARS-CoV-2 Multi-Antigen IgG assay was carried out using well-characterized SARS-CoV-2 reverse transcription polymerase chain reactive positive (97) and pre-COVID-19 pandemic (86) plasma panels. Cross-reactivity was assessed using pre-COVID-19 pandemic plasma specimens (213) from the 2018 Nigeria HIV/AIDS Indicator and Impact Survey (NAIIS).

The overall sensitivity of the xMAP SARS-CoV-2 Multi-Antigen IgG assay was 75.3% [95% CI: 65.8%– 82.8%] and specificity was 99.0% [95% CI: 96.8%– 99.7%]. The sensitivity estimate increased to 83.3% [95% CI: 70.4%– 91.3%] for specimens >14 days post-confirmation of diagnosis. However, using the NAIIS pre-pandemic specimens, the false positivity rate was 1.4% (3/213).

Our results showed overall lower sensitivity and a comparable specificity with the manufacturer’s validation. There appears to be less cross-reactivity with NAIIS pre-pandemic COVID-19 specimens using the xMAP SARS-CoV-2 Multi-Antigen IgG assay. In-country SARS-CoV-2 serology assay validation can help guide the best choice of assays in Africa.