Increase in SARS-CoV-2 RBD-specific IgA and IgG Antibodies in Human Milk from Lactating Women Following the COVID-19 Booster Vaccination

The CDC recommended a booster dose of the Pfizer-BioNTech Comirnaty (BNT162b2) COVID-19 mRNA vaccine in September 2021 for high-risk individuals. Pregnant and high-risk lactating women were encouraged to receive the booster to obtain potential prolonged protection for themselves and their infants. This study investigated the ability of the booster vaccine to increase IgA and IgG antibodies specific to the receptor binding domain (RBD) of the SARS-CoV-2 spike protein in human milk compared to levels pre-booster. We found a significant increase in both anti-RBD-specific IgA and IgG antibodies in human milk 1-2 weeks after the Pfizer-BioNTech booster and at the study endpoint (60 days post-booster). These results suggest the booster vaccination enhances SARS-CoV-2 specific immunity in human breast milk, which may be protective for infants.