Humoral response to anti-SARS-CoV-2 vaccine in breastfeeding mothers and mother-to-infant antibody transfer through breast milk

Abstract

The magnitude of mother-to-infant transfer of anti-SARS-CoV-2 antibodies through breast milk (BM) after maternal vaccination during breastfeeding, in the absence of transplacental transfer of IgG, remains unclear. Here, we quantified anti-S and anti-RBD IgG, IgA, IgA1, and IgA2 in maternal serum, maternal saliva, BM, infant buccal swabs, and infant feces up to 90 days after the second maternal vaccine dose. BNT162b2 vaccine induced long-lasting IgG in maternal serum, but weaker mucosal antibody production, with anti-SARS-CoV-2 IgG and IgA amounts in BM between 10- and 150-fold lower compared to serum. BM IgA were exclusively of the IgA1 isotype, with no production of the mucosal-specific and protease-resistant IgA2. Accordingly, only traces of antibodies were retrieved from the feces of breastfed infants, and no IgG nor IgA were retrieved from infants’ buccal swabs. Newly engineered anti-SARS-CoV-2 vaccines may be needed to stimulate the antibody production at mucosal sites such as breast milk.

COVID-19 Vaccines during Pregnancy and Breastfeeding: A Systematic Review

“…Several authors have studied immunoglobulin A (IgA). An Italian study analyzes the immunity of breastfed babies by mothers vaccinated during lactation [ 47 ]. Only the IgA1 isotype was found in milk, and the study was unable to demonstrate significant mucosal IgA2.…”

“…Only the IgA1 isotype was found in milk, and the study was unable to demonstrate significant mucosal IgA2. The authors did not find a significant amount of antibodies in babies’ buccal swabs or feces [ 47 ]. Thus, they conclude that vaccination induces a strong Immunoglobulin G (IgG) humoral response in maternal serum and is lower in breast milk (10–150 times fewer immunoglobulins in milk than in maternal serum) [ 47 ].…”

“…The humoral response to COVID-19 vaccination has been widely studied [ 17 , 25 , 30 , 32 , 33 , 34 , 36 , 38 , 39 , 41 , 46 , 47 , 50 ]. Recent studies focus on clarifying the mother–child transmission of the cellular response [ 31 , 35 ].…”

“…According to Pietrasanta et al, vaccination induces a stronger immune response in maternal serum than in milk because IgA was not found in infants’ mucosae [ 47 ]. This finding has a physiological reason, as IgA2 is the only one resistant to protease.…”

“…This finding has a physiological reason, as IgA2 is the only one resistant to protease. When authors conclude that the immune response in milk is weaker, they could be underestimating natural passive immunity because the cellular response is not analyzed [ 47 ]. Regarding the evolution of IgA and the age of the newborn, there are contradictory conclusions: from none [ 35 ] to a negative relationship [ 34 ].…”