The COVALAC Study: The Impact of COVID-19 Vaccination During Lactation on SARS-CoV-2-Specific Antibodies in Human Milk-A Prospective Cohort Study.

BACKGROUND

The COVID-19-pandemic prompted global vaccination campaigns, raising important questions about vaccine-induced immune responses in lactating women and the transfer of SARS-CoV-2-specific antibodies through human milk. This study investigated the presence of SARS-CoV-2-specific IgA and IgG antibodies in breastmilk for up to 6 months following COVID-19 vaccination and booster doses with either mRNA or adenoviral vector (AVV) vaccines.

METHOD: The COVALAC-study was a prospective cohort study conducted in Belgium. Women were recruited between February and March 2021, followed for 180 days post-vaccination and 28 days post-booster. Breastmilk samples were collected at multiple timepoints and analyzed for IgA and IgG antibodies. Participants received either mRNA (BNT162b2, mRNA-127) or AVV (ChAdOx1 nCoV-19) vaccines. Antibody concentrations were measured using an in-house immunoassay, and analyses compared responses between vaccine types.

RESULTS

Of the 115 participants, 40% received BNT162b2, 4.3% mRNA-1273, and 55.7% ChAdOx1-S as their primary vaccination. Of these, 31 participants received an mRNA booster (11 homologous, 20 heterologous boosters). IgA and IgG antibody levels were monitored pre- and post-vaccination, showing a stronger antibody response after mRNA vaccination compared to AVV, after roughly 14 days (IgA receptor binding domain [RBD] 1.13 BAU/mil; 0.61-1.67; IgG RBD 2.56 BAU/mil; 0.76-4.71, up to 1 month, for most antibodies. Both homologous and heterologous boosters further increased antibody titers (IgA RBD 0,85 BAU/ml; 1.09-1.72).

CONCLUSION

COVID-19 vaccination during lactating induces SARS-CoV-2 specific IgA and IgG antibodies in human milk. Antibody levels were higher following mRNA vaccination compared to AVV vaccination, with booster doses enhancing these levels further.