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

ImportanceTo 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. DesignGestational 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. SettingLactating healthcare workers living in Singapore ParticipantsConvenience sample of ten lactating healthcare workers. Human milk samples were collected at four time points: pre-vaccination, 1-3 days after dose one, 7-10 days after dose one, and 3-7 days after dose two of the BNT162b2 vaccine. ExposureTwo 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. ResultsTen lactating healthcare workers aged 32.5 years (range 29 - 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 -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. Conclusions and RelevanceIn 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. Trial RegistrationRegistered at clinicaltrials.gov (NCT04802278). Key PointsO_ST_ABSQuestionC_ST_ABSDoes BNT162b2 (i) induce the production and secretion of SARS-CoV-2 specific antibodies into human milk, and/or (ii) get secreted into human milk? FindingsIn this cohort that included ten lactating healthcare workers following BNT162b2 vaccination, 90% produced SARS-CoV-2 immunoglobulin A, and 100% produced immunoglobulin G in human milk, with minimal amounts of vaccine mRNA transfer. MeaningLactating individuals should continue breastfeeding in an uninterrupted manner after receiving SARS-CoV-2 mRNA vaccination.