Women vaccinated against COVID-19 transfer SARS-CoV-2 antibodies to their breastfed infants, potentially giving their babies passive immunity against the coronavirus, according to University of Massachusetts Amherst research.

The study, published in the journal Obstetrics & Gynecology, measured the immune response to the COVID-19 mRNA vaccine in both breast milk and the stools of breastfed infants.

Thirty lactating women from across the U.S. – most of them healthcare workers – were enrolled in the study. They received the COVID-19 mRNA vaccine between January and April 2021. The women provided breast milk samples before they were vaccinated, across two to three weeks after their first vaccine dose and across three weeks after the second dose. They also gave samples of their blood, spotted on cards, 19 days after the first dose and 21 days after the second dose. Infant stool samples were collected 21 days after the mothers’ second vaccination. Pre-pandemic samples of breast milk, dried blood spots and infant stools were used as controls for the study.

The samples were tested for receptor-binding domain (RBD)-specific immunoglobulin (Ig)A and IgG antibodies. In the breast milk samples, anti-RBD IgG antibodies were found to neutralize the protein spike of SARS-CoV-2, as well as four variants. A significant increase in cytokine levels also revealed the immune response in breast milk samples.

Anti-RBD IgG and anti-RBD IgA antibodies were detected in 33% and 30% of infant stool samples, respectively. The levels of antibodies correlated with the vaccine side effects the mother experienced.

Release date: 07 January 2022
Source: University of Massachusetts Amherst

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