Background Serosurveillance is an important method to help monitor COVID-19 in the community in Mali. We previously adapted and qualified a two-antigen Enzyme-Linked Immunosorbent Assays for use in local laboratories using venous blood samples (95% CI, 73.9% (51.6–89.8) and 99.4% (97.7–99.9)) respectively as sensitivity and specificity). However, the burden of blood collection set cost can be challenging in resource limited region where alternative source of biological material will facilitate a large scale of COVID19 surveillance. In this study (funded by NIH) we assessed the of dried blood spot (DBS) samples to quantify Sars-Cov-2 antibodies by ELISA using RBD and Spike antigens.

Methods Respectively 248, 226 and 391 volunteers were randomly selected from Sotuba (urban), Bancoumana (town) and Doneguebougou (village). Venous blood and DBS samples were collected, tested in parallel to assess concordance and the performances of the DBS samples. During the optimization phase (n=36), a promising concordance was found. This allowed us to analyze 829 additional samples on the Spike antigen.

Results We had (31/36) of samples that were COVID-19 seropositive (two category kappa 1.0) in both type of samples, suggesting a strong concordance. Analysis of the 829 samples showed a high correlation (Pearson r = 0.9239 p < 0.0001) with 98% concordance between venous blood ELISA and simplified DBS spike ELISA (kappa = 0.92). As performances, the DBS showed a sensitivity of 99% (95% CI, 98%-99%) and a specificity of 99% (95% CI, 93%-100%). It had 100% (95% CI, 99%-100%) as positive predictive value, 88% (95% CI, 79%-94%) as negative predictive value.

Conclusion Overall, DBS elution and testing was comparable to venous blood testing in the Malian population, and this supports it use in large-scale SARS-CoV-2 serosurveillance studies as a valuable alternative to venipuncture. Our perspective is to optimize/adapt DBS serology to other viruses like Zika virus, Ebola virus, Dengue virus, hepatitis viruses.