Human sera
Human sera were obtained from 5 COVID-19 convalescent patients which were recruited at the University Hospital of Bern, Bern, Switzerland as described (43). Participants were recruited via three different routes: (a) inpatients with a SARS‐CoV‐2 test result (real‐time PCR; RT‐PCR), (b) medical personnel of the Inselspital, and (c) residual material from patients stored at the Liquid Biobank Bern (www.biobankbern.ch). Inclusion criteria of inpatients are (a) hospitalization in Inselspital, (b) tested positive for SARS‐CoV‐2 using RT‐PCR (nasopharyngeal swab), (c) aged 18 or older, and (d) signed general consent.