Immune Response to Vaccination against COVID-19 in Breastfeeding Health Workers

Initially, there were no data on the safety of COVID-19 vaccines in lactating women. The aim of our study was to evaluate the immune response to COVID-19 vaccinations in breastfeeding women.

The study included 32 breastfeeding women who, regardless of the study, had decided to be vaccinated. Maternal serum and breast milk samples were simultaneously collected on days 8 ± 1, 22 ± 2, 29 ± 3, and 43 ± 4 after the first dose of the vaccine. The immune response was assessed by determining the presence of anti-SARS-CoV-2 IgG and IgA.

The breast milk IgG level was detectable (6.50 ± 6.74, median 4.7, and maximum 34.2 BAU/mL) and highly correlated to serum IgG level (r_S 0.89; p < 0.001). The breast milk ratio of IgA to the cut-off value was higher in serum IgA-positive (4.18 ± 3.26, median 2.8, and maximum >10) than in serum IgA-negative women (0.56 ± 0.37, median 0.5, and maximum 1.6; p < 0.001). The highest concentrations of serum and breast milk antibodies were observed on day 29 ± 3 with a decrease on day 43 ± 4.

The immune response to the vaccination against SARS-CoV-2 is strongest 7 ± 3 days after the second dose of the vaccine. Lactating mothers breastfeeding their children after vaccination against SARS-CoV-2 may transfer antibodies to their infant.