Antibodies to the three chemokines with P < 10−4 (CCL19, CCL22 and CXCL17) clustered together and by themselves were sufficient to correctly assign healthy controls and COVID-19 convalescents with high accuracy (96.8%; Fig. 1a–c and Extended Data Fig. 2c,d), so they were defined as a ‘COVID-19 signature’. This evidence concerns the gene CXCL17 and COVID-19.