The antibody response to vaccination and infection is key to immune defense and human antibody therapeutic development, offering a blueprint for targeted treatments. While B-cell sequencing aids human antibody discovery, it may miss the full diversity of circulating antibodies, as only 2-3% of B cells are in circulation, and not all produce antibodies. We demonstrate a mass spectrometry proteomics-based approach to sequencing neutralizing antibodies from serum of a patient vaccinated against SARS-CoV-2. Following de novo sequencing, we recombinantly expressed 12 antibodies. Six recombinant antibodies exhibited similar or higher binding affinities than the original natural polyclonal antibody and exhibited neutralizing capabilities.