Negative SARS-CoV2-antibodies after positive COVID-19-PCR nasopharyngeal swab in patients treated with anti-CD20 therapies. (May 2021) - Friedli, Christoph; Diem, Lara; Hammer, Helly; Kamber, Nicole; Suter-Riniker, Franziska; Leib, Stephen; Chan, Andrew; Hirzel, Cédric; Hoepner, Robert; Salmen, Anke