A Single Drop of Fingerstick Blood for Quantitative Antibody Response Evaluation After SARS-CoV-2 Vaccination

Du, J.; Zhang, D.; May, H.; Loginova, Y.; Chu, E.; Madej, R.; Lu, C. M.; Pathakamuri, J. A.; Kuebler, D.; Neves, J. V.; Zhang, A.; Sha, M. Y.

Among several COVID vaccines that have been approved, the Moderna and Pfizer-BioNTech vaccines are mRNA vaccines that are safe and highly effective at preventing COVID-19 illness. Studies have demonstrated that neutralizing antibody responses elicited by these vaccines correlate strongly with antibodies measured by immunoassays such as ELISA. To monitor the antibody level duration of vaccine-induced immune responses in vaccinated population, cost-effective and easily implementable antibody testing methodologies are urgently needed. In this study, we evaluated the feasibility of using a single drop of fingerstick blood collected with flocked swabs for a high-throughput and quantitative anti-SARS-CoV-2 spike (S1) IgG antibody immunoassay. A total of 50 voluntary subjects participated and donated fingerstick blood samples before and after receiving the Moderna mRNA vaccine. Among all individuals tested, no anti-SARS-CoV-2 S1 IgG antibody was detected before vaccination and on day 7 after receiving the first vaccine dose. On day 14 after the first dose, a significant amount of anti-SARS-CoV-2 S1 IgG antibody was detected in all participants samples. By the end the third week from the first dose, the median anti-SARS-CoV-2 S1 IgG concentration increased to 44.9 ug/mL. No anti-SARS-CoV-2 nucleocapsid (N) protein IgG antibody was detected in any of the participants during the study period, indicating that the anti-SARS-CoV-2 S1 IgG assay is specific for the mRNA vaccine induced antibodies. Comaprison of venous blood plasma and fingerstick blood for anti-SARS-CoV-2 S1 IgG shown a higher correlation. Furthermore, the fingerstick blood dried swab samples are stable for at least 4 days. In summary, we demonstrated that a single drop of fingerstick blood collected with flocked swab can be used for quantitative detection and monitoring of anti-SARS-CoV-2 spike IgG responses after receiving COVID-19 vaccination. This testing platform does not require venous blood draw and can be easily implemented for large scale antibody testing in vaccinated populations.