ABSTRACT: The current COVID-19 pandemic underlines the need for the rapid development of diagnostics and vaccines. Up to now, SARS-CoV-2 provoked more than 130 million infections and more than 2.9 million deaths globally. Antibodies do not only play a critical role in combating infections, but often form the basis for serological diagnostics. Peptide microarrays are an ideal tool to screen large libraries of peptides against serum antibodies on the epitope level. With the goal to identify potential discriminating serological markers for different COVID-19 disease phases (acute and convalescent) and clinical outcomes (mild and severe), we analyzed the epitope-specific antibody responses across the entire proteome of SARS-CoV-2. In a collaboration with the Charité in Berlin, our study identified a NSP15-derived peptide as potential marker for early and/or late COVID-19 disease detection. Moreover, we discovered several epitopes, which were significantly associated with severe COVID-19 disease.