Characterization of SARS CoV-2 Antibodies in Breast Milk from 21 Women with Confirmed COVID-19 Infection

One potential mechanism for protection from SARS-CoV-2 in infants and young children is through passive immunity via breast milk from a mother previously infected with the novel coronavirus. The primary objectives of this study were to establish the presence of SARS-CoV-2 specific IgA and IgG and to characterize the specific antigenic regions of SARS-CoV-2 proteins that were reactive with antibodies in breast milk from women with confirmed SARS-CoV-2 infection. Between March 2020 and September 2020, 21 women with confirmed SARS-CoV-2 infection were enrolled into Mommy’s Milk at the University of California, San Diego. Women donated serial breast milk samples. Breast milk samples were used to probe a multi-coronavirus protein microarray containing full-length proteins and variable length overlapping fragments of SARS-CoV-2 spike (S), envelope (E), membrane (M), nucleocapsid (N), and open reading frame (ORF) proteins. The breast milk samples contained IgA reactive with a variety of SARS-CoV-2 antigens. The most IgA-reactive SARS-CoV-2 proteins were N (42.9% of women responded to 1 ≥ N fragment) and S proteins (23.9% of women responded to ≥ 1 fragment of S1 or S2). Overall, individual COVID-19 cases had diverse and unique milk IgA profiles over the course of follow-up since onset of SARS-CoV-2 symptoms.