COVID-19 mRNA vaccine mediated antibodies in human breast milk and their association with breast milk microbiota composition

Abstract

<p>Newborns can acquire immunological protection to SARS-CoV-2 through vaccine-conferred antibodies in breast milk. However, there are some concerns in lactating mothers with regards to potential short- and long-term adverse events and vaccine-induced changes to their breast milk microbiome composition. This study’s objective was to examine the specific immunity levels in human breast milk following SARS-CoV-2 mRNA vaccination and its associations with breast milk microbiota composition. This study used a longitudinal prospective cohort design. From Jun 2021 and August 2021, we recruited 49 lactating mothers from Hong Kong who had two doses of BNT162b2 vaccine.</p><p><br></p><p>Breast milk samples were collected at 4 different timepoints: pre-vaccination, 1 week post-first dose, 1 week post-second dose, and 1 month post-second dose. Changes in human breast milk microbiota were assessed by 16S rRNA sequencing. Immune responses to BNT162b2, including SARS-CoV-2 spike protein-specific IgA and IgG levels in breast milk at different timepoints. 43 mothers (median age of 36 years) were included in the final analyses. The levels of SARS-CoV-2 spike protein-specific IgA and IgG in breast milk peaked at one week post-second dose. Subsequently, the levels of both antibodies rapidly waned in breast milk, with IgA levels returning to baseline levels one month post-second dose. However, no significant changes were observed in the abundances of beneficial microbes such as <em>Bifidobacterium</em> species after vaccination. We found that the baseline breast milk bacterial composition can predict IgA levels at one week post-second dose (Area Under Curve: 0.72, 95% CI: 0.58–0.85).</p><p>This study shows that anti-SARS-CoV-2 antibody levels in breast milk were boosted after two doses of the BNT162b2 vaccine and rapidly declined thereafter. BNT162b2 vaccine did not significantly change the abundances of beneficial microbes in breast milk, although there is an association between microbiota composition and vaccine-induced antibody levels in breast milk following the vaccination.<br></p>