(HealthDay News) — Breast milk from women vaccinated with the novel mRNA-based Pfizer-BioNTech COVID-19 vaccine contains specific anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin (Ig)G(S1) antibodies, according to a research letter published online Aug. 11 in JAMA Network Open.

Erika Esteve-Palau, M.D., Ph.D., from Parc Sanitari Sant Joan de Déu in Barcelona, Spain, and colleagues characterized the levels of specific SARS-CoV-2 antibodies in the breast milk of 33 mRNA-vaccinated lactating women, as well as their correlation with serum antibody levels.

The researchers found that the median IgG(S1) levels for serum-milk pairs at the three time points were 519 to 1 arbitrary units (AU) per mL at two weeks after the first dose, 18,644 to 78 AU/mL at two weeks after the second dose, and 12,478 to 50.4 AU/mL at four weeks after the second dose. The Pearson correlation coefficient between breast milk and serum levels of IgG(S1) was 0.7.

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“Larger prospective studies examining these issues are needed to confirm the safety of SARS-CoV-2 vaccination in individuals who are breastfeeding and further assess the association of vaccination with infants’ health and SARS-CoV-2-specific immunity,” the authors write.

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