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

Erika Esteve-Palau, MD, PhD, 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 3 time points were 519 to 1 arbitrary units (AU) per mL at 2 weeks after the first dose, 18,644 to 78 AU/mL at 2 weeks after the second dose, and 12,478 to 50.4 AU/mL at 4 weeks after the second dose. The Pearson correlation coefficient between breast milk and serum levels of IgG(S1) was 0.7.

“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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