Anti-SARS-CoV-2 antibodies in breast milk during lactation after infection or vaccination: A cohort study

Abstract

Breast milk is a pivotal source to provide passive immunity in newborns over the first few months of life. Very little is known about the antibody transfer levels over the period of breastfeeding. We conducted a prospective study in which we evaluated concentrations of anti-SARS-CoV-2 Spike IgA and RBD IgG/M/A antibodies in maternal serum and breast milk over a duration of up to 6 months after delivery. We compared antibody levels in women with confirmed COVID-19 infection during pregnancy (n = 16) to women with prenatal SARS-CoV-2 vaccination (n = 5). Among the recovered women, n = 7 (44%) had been vaccinated during the lactation period as well. We observed intraindividual moderate positive correlations between antibody levels in maternal serum and breast milk (r = 0.73, p-value<0.0001), whereupon the median levels were generally higher in serum. Anti-RBD IgA/M/G transfer into breast milk was significantly higher in women recovered from COVID-19 and vaccinated during lactation (35.15 AU/ml; IQR 21.96-66.89 AU/ml) compared to the nonvaccinated recovered group (1.26 AU/ml; IQR 0.49-3.81 AU/ml), as well as in the vaccinated only group (4.52 AU/ml; IQR 3.19-6.23 AU/ml). Notably, the antibody level in breast milk post SARS-CoV-2 infection sharply increased following a single dose of vaccine. Breast milk antibodies in all groups showed neutralization capacities against an early pandemic SARS-CoV-2 isolate (HH-1) and moreover, also against the Omicron variant, although with lower antibody titer. Our findings highlight the importance of booster vaccinations especially after SARS-CoV-2 infection in pregnancy in order to optimize protection in mother and newborn.

Keywords: Antibodies; Breast milk; Humoral immune response; Passive immunity; Pregnancy; SARS-CoV-2.

Fig. 1

Comparison between median antibody levels in serum (triangle) and breast milk (circle) according to the three different groups RV (blue), V (green) and R (red) assessed by anti-S1-RBD-SARS-CoV-2 assay (A), anti-SARS-CoV-2 IgA ELISA (B) and anti- SARS-CoV-2 TrimericS IgG (C). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Comparison between median antibodiy levels in breast milk according to the three different groups RV (blue), V (green) and R (red) assessed by anti-S1-RBD-SARS-CoV-2 assay (A) and anti-SARS-CoV-2 IgA ELISA (B)*p < 0.05, * *p < 0.01, * **p < 0.001, and * ** *p < 0.0001. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

6 months-follow-up post delivery kinetic humoral response of antibodies anti-S1-RBD-SARS-CoV-2 in breast milk according to the R (A) and the RV (B) groups.