The global response to the COVID-19 pandemic has been successfully driven by efforts to ramp up access to vaccines. Pregnant or breastfeeding women and their children have not benefited from the vaccines despite their susceptibility to the virus. We investigated whether women who were offered vaccination after delivery passively transferred protective antibodies to their infants via breast milk. Serum was collected from breast feeding mother-infant pairs and analysed for levels of antibodies to the SARS-CoV-2 spike protein using the CLIA chemiluminescence technique. Data were analysed for the significance of the differences using the Mann-Whitney U test and the Spearman's rank correlation coefficient to determine the strength of the correlation. A total of 13 mothers, mean age 34.86 (95%CI = 33.21-36.48) years and their infants, mean age 15.77 (95%CI = 11.24-20.29) months were enrolled. The mothers had completed their courses of the mRNA BNT162b2 SARS-CoV-2 vaccine during breastfeeding, 8.3 (95%CI = 7.24-9.36) months before the study. All 13 mothers had detectable antibodies to the SARS-CoV-2 spike protein, mean 1252, (95%CI = 736-1769) BAU/mL. Antibodies were detected in 3/13 (23%) breast-fed infants mean 322, (95%CI = 252-897) BAU/mL. There was no correlation between the maternal and infant IgG antibody titres. The time-lag since full vaccination did not correlate to the presence of antibodies in infant sera. Maternal or infant ages did not correlate to the presence of antibodies. Although some children (23%) had anti-SARS-CoV-2 antibodies, there was no association between vaccine-induced COVID-19 spike protein specific maternal IgG antibody titres and the presence of antibodies in the breastfed infants. The data show that the transfer of passive immunity to infants following post-partum vaccination with the mRNA BNT162b2 SARS-CoV-2 vaccine may be infrequent in this population.
Keywords: COVID-19; antibodies; breastfeeding; immunity; infants; vaccination.