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Babies receive boost from breast milk for at least 80 days after mom vaccinated, WashU study shows

The research provides some of the first evidence that babies get a long-lasting immune response through breastfeeding
Credit: evso - stock.adobe.com

ST. LOUIS — Nursing mothers who receive a COVID-19 vaccination may pass protective antibodies through their breast milk for at least 80 days after being vaccinated, according to new research from the Washington University School of Medicine.

“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 Dr. Jeannie Kelly, assistant professor of obstetrics and gynecology. “The antibody levels were still high at the end of our study, so the protection likely extends even longer.”

Although other research has shown that COVID-19 vaccines generate antibodies that are passed to nursing infants through breast milk, this is thought to be the first study to track specific levels of antibodies in breast milk over an extended time.

The study, published March 30 in the American Journal of Obstetrics and Gynecology, tracked levels of COVID-19 antibodies in breast milk from a baseline before the mothers’ first vaccinations and on a weekly basis for 80 days after those initial shots.

The small study involved five mothers who provided frozen breast milk samples after receiving the two-dose Pfizer-BioNTech vaccine. The research 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.

“There is so much vaccine misinformation out there right now – really scary, misleading posts on social media that are designed to scare moms – so we felt like we needed to look at the science,” Kelly said. “We know that these types of antibodies coat babies’ mouths and throats and protect against disease when a baby is drinking breast milk. So, getting vaccinated while breastfeeding not only protects mom, but also could protect the baby, too, and for months.”

The babies of women included in the study ranged in age from 1 month to 24 months old. To gauge immune response in the breast milk, researchers monitored levels of the immunoglobulins IgA and IgG, which are antibodies deployed by the immune system to fight infections.

Results confirm that breast milk contains elevated levels of the IgA and IgG antibodies immediately following the first dose of vaccination, with both antibodies reaching immune-significant levels within 14 to 20 days of first vaccination in all participants.

“Our paper is the first that has shown COVID-19 antibodies persist in breast milk for months following the mother’s vaccination,” said the study’s senior author, Dr. Misty Good, an assistant professor of pediatrics at Washington University.

Kelly said that even though a COVID-19 infection is more severe during pregnancy, there have been almost 70,000 pregnant people vaccinated against COVID-19 with no evidence of harm.

“We’re now seeing a cascade of new data that indicate maternal vaccines are also going to help protect babies — both through transfer of antibodies through the placenta during pregnancy and through the breast milk during lactation,” Kelly said. “This is information we didn’t have a few months ago, and it’s really helping us better counsel our patients who are considering getting the vaccine. I’m telling my pregnant and breastfeeding moms that I strongly recommend that they get vaccinated as soon as possible.”