Study Finds COVID-19 Antibodies in Breast Milk of Vaccinated Mothers

Mothers vaccinated against COVID-19 produced robust IgG antibodies in breast milk that actively neutralized the SARS-CoV-2 virus, according to investigators.

Mothers with immunity from COVID-19—either acquired after recovery from infection or acquired via mRNA vaccination—produced breast milk containing active SARS-CoV-2 antibodies, according to research published November 10 online in the journal JAMA Pediatrics.

Both the IgA-dominant response to infection and the IgG-dominant response to vaccination were associated with production of human milk that exhibited neutralization against live SARS-CoV-2 virus.

Researchers from the University of Rochester Medical Center (URMC) and New York University state in a URMC press release that the finding represents the first time this type of evidence has been discovered for both IgA and IgG antibodies.

“It’s one thing to measure antibody concentrations, but it’s another to say that antibodies are functional and can neutralize the SARS-CoV-2 virus,” said co-author Bridget Young, PhD, assistant professor in the Division of Pediatric Allergy and Immunology at URMC. “One of the exciting findings in this work is that breast milk from both mothers with COVID-19 infection, and from mothers receiving mRNA vaccination contained these active antibodies that were able to neutralize the virus.”

Past URMC research had shown evidence of antibodies in breast milk from mothers who tested positive for COIVD-19, according to the statement, but the current, follow-up study reflects the longest period of time during which disease-acquired antibodies have been examined after recovery from illness. According to the study, the antibodies exist for 3 months after infection.

For vaccinated mothers, researchers note, there was a mild-to-moderate decline in antibodies an average of 3 months after vaccination.

Investigators recruited convenience samples of lactating mothers for the infection and vaccinated cohorts.

The post-infection cohort study was conducted between July 2020 and April 2021 and included individuals aged 18 years or older with PCR-confirmed COVID-19 diagnosis within the previous 14 days who were currently lactating and had an infant age 6 months or younger. These participants collected breast milk samples in their home on day 0 (the day they received collection materials), and subsequently on days 3, 7, 10, 28, and 90.

Vaccinated participants, studied between December 2020 and May 2021, were health care professionals receiving a first does of either the Pfizer or Moderna mRNA vaccine between December 2020 and January 2021 and were lactating with an infant of any age. The participants provided a sample of breast milk before the first vaccine dose, 18 days after the first dose, again 18 days after the second vaccine dose, and 90 days after the second dose.

The final group numbered 77—47 mothers in the infected group, 30 in the vaccinated group. Mean (SD) age of participants in the infection group was 29.9 (4.4) years and in the vaccinated group 33.0 (3.4) years, respectively. Infants in the infection group had a mean (SD) age of 3.1 (2.2) months and in the vaccinated group of 7.5 (5.2) months. The majority of participants overall were white. Among vaccinated mothers, (40%) received the Pfizer vaccine and (51%) the Moderna shot.

Summary of Findings

Full details of the varying kinetics and concentrations of anti-SARS-oV-2 antibodies between the 2 groups of mothers are available in the study, online. In summary, COVID-19 infection was associated with a relatively universal rapid and long-lasting IgA response vs a more variable IgG response. Conversely, IgA response in human milk after vaccination was initially lower, increased after the first vaccine dose, then decreased after the second shot. The human milk IgG response to vaccination, however, was both larger and more stable vs post-infection lactating mothers.

Neutralizing activity was seen in human milk from both groups with activity slightly higher in the infection group.

“The trend in breast milk antibodies aligns with what we see in vaccination sera,” said study co-author Kirsi Jarvinen-Seppo, PhD, M.D., Chief of Pediatric Allergy and Immunology at URMC, in the university statement. “After a few months, the antibodies trend downward, but the levels are still significantly above what they were pre-vaccine.”

The investigators caution against supposing that because the antibody response exists, that breast milk antibodies can provide protection against COVID for nursing children.

“The study does not imply that children would be protected from illness,” said Jarvinen-Seppo, “and breast milk antibodies may not be a substitute for vaccination for infants and children, once approved.”

The next phase of the study, say URMC researchers, will look for evidence of whether both vaccination and illness-acquired immunity provide antibodies against other seasonal coronaviruses.


Reference: Young BE, Seppo AE, Diaz N, et al. Association of human milk antibody induction, persistence, and neutralizing capacity with SARS-CoV-2 infection vs mRNA vaccination. JAMA Pediatr. Published online November 10, 2021.