Codominant IgG and IgA expression with minimal vaccine mRNA in milk of BNT162b2 vaccinees

Low, Jia Ming; Gu, Yue; Ng, Melissa Shu Feng; Amin, Zubair; Lee, Le Ye; Ng, Yvonne Peng Mei; Shunmuganathan, Bhuvaneshwari D/O; Niu, Yuxi; Gupta, Rashi; Tambyah, Paul Anantharajah; MacAry, Paul A.; Wang, Liang Wei; Zhong, Youjia

Lactating women can produce protective antibodies in their milk after vaccination, which has informed antenatal vaccination programs for diseases such as influenza and pertussis. However, whether SARS-CoV-2-specific antibodies are produced in human milk as a result of COVID-19 vaccination is still unclear. In this study, we show that lactating mothers who received the BNT162b2 vaccine secreted SARS-CoV-2-specific IgA and IgG antibodies into milk, with the most significant increase at 3–7 days post-dose 2. Virus-specific IgG titers were stable out to 4–6 weeks after dose 2. In contrast, SARS-CoV-2-specific IgA levels showed substantial decay. Vaccine mRNA was detected in few milk samples (maximum of 2 ng/ml), indicative of minimal transfer. Additionally, infants who consumed post-vaccination human milk had no reported adverse effects up to 28 days post-ingestion. Our results define the safety and efficacy profiles of the vaccine in this demographic and provide initial evidence for protective immunity conferred by milk-borne SARS-CoV-2-specific antibodies. Taken together, our study supports recommendations for uninterrupted breastfeeding subsequent to mRNA vaccination against COVID-19.