Receptor‐binding Domain Severe Acute Respiratory Syndrome Coronavirus 2‐specific Antibodies in Human Milk From Mothers With Coronavirus Disease 2019 Polymerase Chain Reaction or With Symptoms Suggestive of Coronavirus Disease 2019

ABSTRACT This study aims to compare the receptor‐binding domain (RBD) severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2)‐specific antibody titers in human milk between mothers with a confirmed coronavirus disease 2019 (COVID‐19) polymerase chain reaction (PCR) test and mothers with viral symptoms suggestive of COVID‐19. The area under the curve (AUC) for RBD SARS‐CoV‐2‐specific secretory immunoglobulin A (SIgA)/immunoglobulin A (IgA), secretory immunoglobulin M (SIgM)/immunoglobulin M (IgM), immunoglobulin G (IgG), and free secretory components (fSC) in milk samples from eight mothers with a confirmed COVID‐19 PCR, eight mothers with viral symptoms (no PCR testing), and six unexposed mothers (pre‐pandemic 2018). AUCs of RBD SARS‐CoV‐2‐specific SIgA/IgA, SIgM/IgM, IgG, and fSC in milk samples were comparable between mothers with confirmed COVID‐19 PCR and mothers with viral symptoms of suggestive COVID‐19. AUCs of RBD‐specific SIgA/IgA, IgG, and fSC were higher in the COVID‐19‐exposed group than in the unexposed group, and SIgM/IgM tended to be higher in the exposed mothers. In conclusion, women with viral symptoms suggestive of COVID‐19 could secrete antibodies and fSC specific to SARS‐CoV‐2 in human milk.