In the first nine months of the pandemic, according to Unicef dearThis left researchers struggling to answer a critical question: Can the virus be transmitted through breast milk? Some people thought it could. But like different groups of researchers they tested the milk, found no traces of the virus, only antibodies – suggesting that drinking milk might protect babies from infection.
The next big question for breast milk researchers was whether the protective benefits of a Covid vaccine could be passed on to babies in the same way. None of the vaccine studies included pregnant or breastfeeding women, so the researchers needed to find lactating women who were eligible for the initial rollout of the vaccine.
Through a Facebook group, Rebecca Powell, a breastmilk immunologist at the Icahn School of Medicine at Mount Sinai in Manhattan, found hundreds of doctors and nurses willing to periodically share their breastmilk. In her most recent study, which has not been formally published, she analyzed the milk of six women who received the Pfizer-BioNTech vaccine and four who received the Moderna vaccine, 14 days after the women received their second injection. She found significant numbers of one particular antibody, called IgG, in all cases. Other researchers have had similar results.
"There is reason to be excited," said Dr. Kathryn Gray, a maternal fetal medicine specialist at Brigham and Women's Hospital in Boston, who conducted similar studies. "We would assume that could provide some level of protection."
But how do we know for sure? One way to test this – exposing babies to the virus – is unethical, of course. Instead, some researchers have tried to answer the question by studying the properties of the antibodies. Are they neutralizing, meaning they prevent the virus from infecting human cells?
In a draft small study, an Israeli researcher found this to be the case. "Human milk has the ability to prevent the spread of viruses and to block the virus' ability to infect host cells, which will lead to disease", Yariv wine, an applied immunologist at Tel Aviv University, wrote in an email.
However, research is too premature for vaccinated breastfeeding mothers to pretend their babies can't get infected, said Dr. Kirsi Jarvinen-Seppo, chief of childhood allergy and immunology at the University of Rochester Medical Center. Dr. Jarvinen-Seppo has conducted similar studies. "There is no direct evidence that the Covid antibodies in breast milk protect the baby – only evidence to suggest that this may be the case," she said.