Factors Influencing Breast Milk Antibody Titers during the Coronavirus Disease 2019 Pandemic: An Observational Study

Abstract

The COVID-19 pandemic has highlighted the role of breastfeeding in providing passive immunity to infants via specific anti-SARS-CoV-2 antibodies in breast milk. We aimed to quantify these antibodies across different lactation stages and identify influencing factors. This prospective study involved mother-child dyads from Innsbruck University Hospital, Austria, with a positive maternal SARS-CoV-2 test during pregnancy or peripartum between 2020 and 2023. We collected breast milk samples at various lactation stages and analyzed anti-Spike S1 receptor-binding domain (S1RBD) immunoglobulins (Ig). Maternal and neonatal data were obtained from interviews and medical records. This study included 140 mothers and 144 neonates. Anti-S1RBD-IgA (72.0%), -IgG (86.0%), and -IgM (41.7%) were highly present in colostrum and decreased as milk matured. Mothers with natural infection and vaccination exhibited higher anti-S1RBD-IgA and -IgG titers in all milk stages. Mothers with moderate to severe infections had higher concentrations of anti-S1RBD-IgA and -IgG in transitional milk and higher anti-S1RBD-IgA and -IgM in mature milk compared to those with mild or asymptomatic infections. Variations in antibody responses were also observed with preterm birth and across different virus waves. This study demonstrates the dynamic nature of breast milk Ig and underscores the importance of breastfeeding during a pandemic.

Keywords: COVID-19; SARS-CoV-2; anti-S1RBD immunoglobulins; breast milk; breastfeeding; immunonutrition.

Figure 1

Concentrations of anti-SARS-CoV-2-S1RBD immunoglobulins (Ig) in different types of breast milk. This figure shows boxplots of anti-S1RBD-IgA, -IgG, and -IgM concentrations in various types of breast milk, including colostrum, transitional milk, and mature milk. Ig concentrations are plotted on the y-axis in U/mL. Center lines in boxes represent medians, box edges mark 1st and 3rd quartiles, and whiskers indicate 10th and 90th percentiles. Individual points indicate outliers. Crosses indicate mean Ig concentrations. The data in the box highlight the dynamic changes in breast milk Ig levels over the lactation period, with the highest median concentrations observed in colostrum and gradually decreasing median concentrations in transitional and mature milk. Ig, immunoglobulin; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; S1RBD, SARS-CoV-2 Spike protein S1 receptor-binding domain.

Figure 2

Concentrations of anti-SARS-CoV-2-S1RBD immunoglobulins (Ig) in breast milk across different SARS-CoV-2 waves. This panel displays boxplots of anti-S1RBD-IgA, -IgG, and -IgM concentrations in different types of breast milk (colostrum, transitional milk, and mature milk) across several waves of the SARS-CoV-2 pandemic. Ig concentrations are plotted on the y-axis in U/mL. Center lines in boxes represent medians, box edges mark 1st and 3rd quartiles, and whiskers indicate 10th and 90th percentiles. The influence of different SARS-CoV-2 waves on breast milk Ig concentrations is depicted. Significant differences across different pandemic waves are indicated by asterisks (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001). Ig, immunoglobulin; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; S1RBD, SARS-CoV-2 Spike protein S1 receptor-binding domain.