Mothers’ COVID-19 Vaccines Can Also Protect Breastfeeding Infants

There have now been approximately 70,000 pregnant people vaccinated against COVID-19 with no evidence of harm.

Nursing mothers who receive a COVID-19 vaccine may pass protective antibodies to their infants through breast milk for at least 80 days following vaccination, according to researchers at the Washington University School of Medicine in St. Louis.

The study involved 5 mothers who provided frozen breast milk samples after receiving the 2-dose COVID-19 vaccine from Pfizer and BioNTech. This is some of the first peer-reviewed evidence that breastfeeding confers a long-lasting immune response in nursing infants and toddlers, according to the study authors.

“Our study showed a huge boost in antibodies against the COVID-19 virus in breast milk starting 2 weeks after the first shot, and this response was sustained for the course of our study, which was almost 3 months long,” said first author Jeannie Kelly, MD, assistant professor of obstetrics and gynecology, in a press release. “The antibodies levels were still high at the end of our study, so the protection likely extends even longer.”

Published March 30 in the American Journal of Obstetrics and Gynecology, the researchers 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 afterward. According to the press release, this is believed to be the first study to track specific levels of these antibodies in breast milk over an extended time period.

“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 really needed to look at the science,” Kelly said in the press release. “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 the women included in the study ranged in age from 1 month to 2 years old. To measure immune response in the breast milk, the investigators monitored levels of the immunoglobulins IgA and IgG, which are deployed by the immune system to fight infections in babies.

Their findings confirm that breast milk contains elevated levels of these antibodies immediately following the first dose of vaccination, with body antibodies reaching immune-significant levels within 14 to 20 days following the first vaccination in all participants. The findings are similar to prior studies on maternal vaccination, which have shown high levels of antibodies in breast milk for up to 6 months following vaccination for influenza and whooping cough.

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

Although further studies of maternal COVID-19 vaccination are needed in order to characterize the length of antibody production in breast milk and the impact on infant infection rates, the investigators said recent research continues to confirm that the COVID-19 vaccine offers real benefits for protecting both mother and child.

Kelly noted that research has confirmed that COVID-19 is more severe during pregnancy and the major benefit of vaccination is to provide protection for mothers before they become severely ill. She added that there have now been approximately 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 in the press release. “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.”


For breastfeeding moms, COVID-19 vaccinations may also protect babies [news release]. Washington University School of Medicine in St. Louis; April 6, 2021. Accessed April 16, 2021.