AbstractObjectivesAs coronavirus disease 2019 (COVID-19) continuous to spread, the transfer of maternal anti severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies via lactation is an important source of immunity in newborns that requires more comprehensive studies to improve vaccine options in these candidates. The aim of this study was to evaluate SARS-CoV-2 spike protein antibodies against COVID-19 in breast milk and serum of lactating mothers post vaccination and to establish a correlation between both.MethodsHundred and eighty lactating mothers were included in this cross sectional cohort study conducted at Rehman Medical Institute, Peshawar. We described the immunogenicity 21 days after the booster dose of vaccine in 21 patients. Breast Milk and serum specimens were collected and investigated for SARS-CoV-2 spike protein antibodies by consuming electro-chemiluminescence immunoassay (Elecsys Anti-SARS-CoV-2 S Roche, Switzerland).ResultsOne-hundred percent of patients revealed robust positive findings to SARS-CoV-2 spike proteins antibodies in breast milk and 85 percent in serum, i.e., >0.8 IU/mL. Our study shows that lactating mothers can mount robust immune reactions against SARS-CoV-2 post vaccination.ConclusionsAll participants had significantly higher antibody titers against SARS-CoV-2 after vaccination. Participants had antibody titers one scale higher post vaccination than pre vaccination. A significant correlation was found between SARS-CoV-2 antibodies in milk and serum. Constant monitoring of antibodies titers is estimated to attain significant humoral immunity against SARS-CoV-2 infection.