Erytra blood group analyser and kode technology testing of SARS‐CoV‐2 antibodies among convalescent patients and vaccinated individuals

Surveillance of the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic requires tests to monitor antibody formation and prevalence. We detected SARS‐CoV‐2 antibodies using red cells coated by Kode technology with short peptides derived from the SARS‐CoV‐2 spike protein (SP). Such modified red cells, called C19‐kodecytes, can be used as reagent cells in any manual or automated column agglutination assay. We investigated the presence of SARS‐CoV‐2 antibodies in 130 samples from COVID‐19 convalescent plasma donors using standard manual technique, two FDA‐authorized enzyme‐linked immunosorbent assay (ELISA) assays and a virus neutralisation assay. The sensitivity of the C19‐kodecyte assay was 88%, comparable to the anti‐SP and anti‐nucleocapsid protein (NCP) ELISAs (86% and 83%) and the virus neutralisation assay (88%). The specificity of the C19‐kodecyte assay was 90% (anti‐SP 100% and anti‐NCP 97%). Likewise, 231 samples from 73 vaccinated individuals were tested with an automated analyser, and we monitored the appearance and persistence of SARS‐CoV‐2 antibodies. The C19‐kodecyte assay is a robust tool for SARS‐CoV‐2 antibody detection. Automated blood group analyser use enables large‐scale SARS‐CoV‐2 antibody testing for vaccination monitoring in population surveys.