Breastfeeding infants receive neutralizing antibodies and cytokines from mothers immunized with a COVID-19 mRNA vaccine

Abstract

Objective: To evaluate the immune response to COVID-19 mRNA-based vaccines present in breastmilk and the transfer of the immune response to the breastfeeding child. Methods: A prospective cohort study enrolled 30 lactating women who received an mRNA-based COVID-19 vaccine between January and April 2021. Women provided serial milk samples, which included milk expressed before vaccination, milk expressed across 2-3 weeks after the first dose, and milk expressed across 3 weeks after the second dose. Women also were asked to provide their blood, spotted on cards (dried blood spots; DBS) 19 days after the first dose and 21 days after the second dose. Stool samples from the breastfed infants were collected 21 days after mothers received their second dose. Pre-pandemic samples of milk, DBS cards, and infant stool from prior studies were also utilized. Milk and infant stool samples were tested by ELISA for receptor-binding domain (RBD)-specific IgA and IgG. Milk samples were tested for the presence of neutralizing antibodies against the spike and four variants of concern (VOCs): D614G, B.1.1.7 (alpha), B.1.351 (beta), and P.1 (gamma). Milk samples were also tested by electrochemiluminescence assay for levels of 10 cytokines. Results: Milk from COVID-19-immunized women neutralized the spike and four VOCs and this response is primarily IgG-driven. The immune response in milk also included significantly elevated levels of interferon-γ (IFN-γ). The immune response to maternal vaccination was reflected in breastfed babies; anti-RBD IgG and anti-RBD IgA was detected in 33% and 30% of infant stool samples, respectively. Levels of anti-RBD antibodies in infant stool correlated with maternal vaccine side-effects. Conclusion: Humoral and cellular immune responses to mRNA-based COVID-19 vaccination are present in the breastmilk of most women. The milk anti-RBD antibodies can neutralize SARS-CoV-2 spike and VOCs. Importantly, we describe for the first time the transfer of anti-RBD antibodies to breastfed infants, with the potential to confer passive immunity against SARS-CoV-2

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

“…To the best of our knowledge, a limited amount of salivary/buccal mucosa antibodies has been recently demonstrated in breastfed infants after maternal infection, not after vaccination, and the presence of these immunoglobulin has been attributed by the authors to the direct activation of neonatal immune system against BM SARS-CoV-2 -Ig immune complexes 29 . Furthermore, only a pre-print, not peer reviewed report of fecal anti-SARS-CoV-2 antibodies recovered in breastfed neonates after maternal COVID-19 vaccination exists 30 : again, the authors did not report an absolute quantification of antibodies, nor a direct quantitative comparison between serum, milk, and fecal concentrations. Thus, it is virtually impossible to establish the real magnitude of this presumed antibody-transfer.…”