The findings showed that breast milk contained elevated levels of the IgA and IgG antibodies -- antibodies deployed by the immune system to fight infections in babies -- immediately following the first dose of vaccination.
Both antibodies reached immune-significant levels within 14 to 20 days of first vaccination in all participants, according to the study, published in the American Journal of Obstetrics and Gynecology.
"Our study showed a huge boost in antibodies against the Covid-19 virus in breast milk starting two weeks after the first shot, and this response was sustained for the course of our study, which was almost three months long," said lead author Jeannie Kelly, Assistant Professor of obstetrics and gynecology at Washington University School of Medicine in St Louis, the US.
"The antibodies levels were still high at the end of our study, so the protection likely extends even longer," Kelly added.
The study involved five mothers who provided frozen breast milk samples after receiving the two-dose Pfizer-BioNTech coronavirus vaccine. They were tracked for antibodies before the first vaccinations and on a weekly basis for 80 days after it.
"Our study is limited by a small number of participants, but the findings provide encouraging news about the potential immune benefit to breast-feeding infants after vaccination," said Misty Good, Assistant Professor of pediatrics, at the Washington University.
The findings provides some of the first peer-reviewed evidence that breastfeeding confers a long-lasting immune response in the nursing infants and toddlers of vaccinated mothers, the researchers said.
While further studies of maternal Covid-19 vaccination are needed to characterize the length of antibody production in breast milk and the effect on infant infection rates, recent research continues to confirm that the Covid-19 vaccine offers real benefits for protecting both mother and child.