Abstract

Background: Activating the specific immune system by vaccination against COVID-19 is crucial to strive against this pandemic. Constant and efficient monitoring of IgG antibody titres is valuable for evaluating immunizations. However, serum or plasma samples, commonly used in follow-up active immunizations, require a visit to the doctor´s office to be handled as a biohazard and need cold chain transportation and storage.
Methods: In contrast, dry blood spots can be self-collected and represent a minimal biohazard potential, even if they contain human pathogenic viruses. Blood sampling was performed on 12 volunteers (8 females) for six months after vaccination. Whole blood drops from a finger pulp were applied on filter paper cards or collected in a Microvette for serum samples. Analysis was performed with a COVID-19 enzyme-linked immunosorbent assay.
Results: The comparison between dry blood spots and serum samples yielded similar results for SARSCoV- 2 IgG antibody titres. Daily blood sampling from the same subject revealed an initial boost in the generation of antibody titres that descended after a peak level. Monitoring convalesced subjects after a COVID-19 infection resulted in SARS-CoV-2 IgG antibody-titres of the same magnitude or higher as vaccinated patients with at least three immunizations. An unvaccinated subject without infection showed SARS-CoV-2 IgG antibody constantly titres below the cutoff level of the assay during the whole observation period.
Conclusion: These results indicate that monitoring SARS-CoV-2 IgG antibody titres from dry blood spot excisions is a user-friendly and reliable technique with a minimal biohazard risk regarding the transport and analysis of these samples.

Keywords:Dry blood cards; COVID-19; Antibody titre; Populations immunity; SARS-CoV-2; Serum