COVID-19 mRNA vaccine-mediated antibodies in human breast milk and their association with breast milk microbiota compositionOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study examined whether the COVID-19 mRNA vaccine BNT162b2 changes the composition of human breast milk microbiota during a two-dose vaccination regimen. It also examined how any such changes relate to the levels of SARS-CoV-2 spike-specific antibodies present in breast milk. The researchers tracked antibody levels and microbiota composition across several time points relative to vaccination, motivated by concerns that maternal mRNA vaccination could affect the breast milk microbiome that helps shape the early-life infant microbiome.
Who was studied?
The study enrolled 49 lactating mothers from Hong Kong who received two doses of the BNT162b2 mRNA vaccine between June 2021 and August 2021. Each participant self-collected breast milk samples at four time points: before vaccination, one week after the first dose, one week after the second dose, and one month after the second dose. The abstract does not report additional demographic details about the cohort.
What were the most important findings?
Levels of SARS-CoV-2 spike-specific IgA and IgG in breast milk peaked one week after the second vaccine dose, then rapidly waned, with IgA returning to baseline by one month post-second dose. The richness and overall composition of breast milk microbiota changed dynamically across the vaccination timeline. However, the abundance of beneficial microbes such as Bifidobacterium species did not significantly change following vaccination. The abstract does not mention Bacteroides fragilis, polysaccharide A, or the B. fragilis toxin, so these are not part of this study's findings.
What are the greatest implications of this study?
The findings suggest that maternal BNT162b2 vaccination generates a transient but measurable antibody response in breast milk that could offer newborns temporary passive immunity to SARS-CoV-2. The preservation of beneficial Bifidobacterium abundance despite shifts in overall microbiota composition suggests the vaccine does not compromise a key beneficial component of the breast milk microbiome. These results may help reassure lactating mothers and clinicians about the microbiome safety of mRNA vaccination during lactation, while the observed waning of antibodies points to a limited window of passive protection for infants.