BNT162b2 vaccination induces SARS-CoV-2 specific antibody secretion into human milk with minimal transfer of vaccine mRNA

Low, J. M.; Gu, Y.; Ng, M. S. F.; Zubair, A.; Lee, L. Y.; Ng, Y. P. M.; DO Shunmuganathan, B.; Niu, Y.; Gupta, R.; Tambyah, P. A.; Macary, P. A.; Wang, L. W.; Zhong, Y.

Importance: To examine the impact of SARS-CoV-2 vaccination of lactating mothers on human milk Objective: (1) To quantify SARS-CoV-2-specific immunoglobulin A (IgA) and immunoglobulin G (IgG) in human milk of lactating mothers who received the BNT162b2 vaccine, with reference to a cohort convalescent from antenatal COVID-19, and healthy lactating mothers. (2) To detect and quantify vaccine mRNA in human milk after BNT162b2 vaccination. Design: Gestational Immunity For Transfer 2 (GIFT-2) is a prospective cohort study of lactating mothers who were due to receive two doses of BNT162b2 vaccine, recruited between 5th February 2021 and 9th February 2021. Setting: Lactating healthcare workers living in Singapore Participants: Convenience sample of ten lactating healthcare workers. Human milk samples were collected at four time points: pre-vaccination, 1 to 3 days after dose one, 7 to 10 days after dose one, and 3 to 7 days after dose two of the BNT162b2 vaccine. Exposure: Two doses of the BNT162b2 vaccine 21 days apart. Main Outcome and Measure: (i) SARS-CoV-2-specific IgA and IgG in human milk of lactating mothers who received BNT162b2 vaccine, (ii) Detection and quantification of vaccine mRNA in human milk after BNT162b2 vaccination. Results: Ten lactating healthcare workers aged 32.5 years (range 29 to 42) were recruited, with 40 human milk samples collected and analysed. SARS-CoV-2-specific IgA was predominant in human milk of lactating mothers who received BNT162b2 vaccine. The sharpest rise in antibody production was 3 to 7 days after dose two of the BNT162b2 vaccine, with medians of 1110 picomolar of anti-SARS-CoV-2 spike and 374 picomolar of anti-Receptor Binding Domain IgA. Vaccine mRNA was detected only on rare occasions, at a maximum concentration of 2 ng/mL. Infants had no reported adverse events, up to 28 days after ingestion of post-vaccination human milk. Conclusions and Relevance: In this cohort of ten lactating mothers following BNT162b2 vaccination, nine (90%) produced SARS-CoV-2 IgA, and ten (100%) produced IgG in human milk with minimal amounts of vaccine mRNA. Lactating individuals should continue breastfeeding in an uninterrupted manner after receiving mRNA vaccination for SARS-CoV-2.