In the first nine months of the pandemic, around 116 million babies were born worldwide, according to Unicef estimates. This left researchers scrambling to answer a critical question: Could the virus be transmitted through breast milk? Some people assumed it could. But as several groups of researchers tested the milk, they found no traces of virus, only antibodies — suggesting that drinking the milk could protect babies from infection.
The next big question for breast milk researchers was whether the protective benefits of a Covid vaccine could be similarly passed to babies. None of the vaccine trials included pregnant or breastfeeding women, so researchers had to find lactating women who qualified for the first vaccine rollout.
Through a Facebook group, Rebecca Powell, a human milk immunologist at the Icahn School of Medicine at Mount Sinai in Manhattan, found hundreds of doctors and nurses willing to periodically share their breast milk. In her most recent study, which has not been formally published, she analyzed the milk of six women who had received the Pfizer-BioNTech vaccine and four who had received the Moderna vaccine, 14 days after the women had received their second shots. She found significant numbers of one particular antibody, called IgG, in all of them. 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 has conducted similar studies. “We’d presume that could confer some level of protection.”
But how do we know for sure? One way to test this — exposing those babies to the virus — is, of course, unethical. Instead, some researchers have tried to answer the question by studying the antibodies’ properties. Are they neutralizing, meaning they prevent the virus from infecting human cells?
In a draft of a small study, one Israeli researcher found that they were. “Breast milk has the capacity to prevent viral dissemination and block the ability of the virus to infect host cells that will result in illness,” Yariv Wine, an applied immunologist at Tel Aviv University, wrote in an email.
Research is too premature for vaccinated mothers who are breastfeeding to act as if their babies can’t get infected, however, said Dr. Kirsi Jarvinen-Seppo, the chief of pediatric allergy and immunology at the University of Rochester Medical Center, who has been conducting similar studies. “There is no direct evidence that the Covid antibodies in breast milk are protecting the infant — only pieces of evidence suggesting that could be the case,” she said.