What Immunity Do Breast Milk Antibodies Confer?

Patient Presentation
A 6-month-old male came to clinic for his health supervision visit. He had been relatively well except for one ear infection and two upper respiratory infections since starting childcare. His mother was concerned about also giving influenza and COVID vaccines in addition to his regular vaccines.

The pertinent physical exam showed a healthy, smiling infant with growth parameters at the 10% for height and 50% for weight and head circumference. He had some rhinorrhea, and his ears were normal as was the rest of his examination.

The diagnosis of a healthy infant with rhinorrhea was made. The mother stated that as she was breastfeeding that was all of the immunity that the baby needed for influenza and COVID. The pediatrician noted that breast milk was really good at helping prevent some diseases but that the baby needed his own immunity from his own vaccines. “I think it is great that you continue to breastfeed, and the milk does give him some immunity, but it isn’t his own and won’t last long term. I know that his brother is coming in next week. I have some good information about the vaccines and immunity that I can give you. Then you and Dad can talk and we can have another discussion next week,” she offered. The patient’s clinical course revealed that the mother was willing to do influenza vaccine the following week for both children but still declined the COVID vaccine as she wanted to do more research into it.

Breast milk (BM) has many benefits including its primary role providing appropriate nutrition for newborns and infants, which includes making those nutrients more bioavailable. While BM does not provide all of the nutritional needs over the entire year or two of breastfeeding, complimentary foods are important for furnishing additional nutritional needs along with helping development of appropriate taste and texture acceptance, along with oral-motor skills. Complimentary foods are recommended by the American Academy of Pediatrics when the infant is developmentally ready which is commonly after 6 months of life. Breastfeeding and BM are also associated with other decreased health risks such as diabetes, obesity, allergies, and sudden infant death syndrome. It also helps prevent infections especially in the gastrointestinal tract directly but others more indirectly.

A review about how much a newborn should eat, can be found here.

Learning Point
Maternal antibodies pass to an infant in two basic ways:

  • Transplacental transfer
    • Mainly IgG passing directly into the fetus and newborn’s serum
    • Half-life is 21 days so this immunity wanes over the first year
    • Provides systematic immunity
    • Protects against a variety of infections including influenza, pertussis, and tetanus
    • Transplacental IgE may play a role in allergic response
  • BM antibodies
    • Is secretory IgA (the main antibody with a half-life of days to a couple of weeks), IgM and some IgG
    • Provides important mucosal immunity, but does not provide systemic immunity as mucosal surfaces including the gut close very soon after birth
    • “…BM antibodies [are important] in the protection of newborns against neonatal infections, seeding the gut microbiome, and training tolerance toward mucosal antigens…”
    • The precise role as to how the BM antibodies assist in these roles is not totally understood but appears to be through a complex variety of ways including passive immunity within the gastrointestinal tract

Data for Coronavirus 19 (COVID-19) is being generated. There is data that supports high rates of IgA and IgG production in BM after maternal COVID-19 immunization including the initial dose. Data regarding its persistence over time within BM, especially after full maternal immunization, and its actual functional impact on disease prevention in infants still remain open questions.

As maternal transplacental and BM antibodies wane over time, infants should receive their own immunizations to retain their own immunity.

Questions for Further Discussion
1. What are contraindications to breastfeeding? A review can be found here
2. How much breast milk does a lactating woman make? A review can be found here
3. What are the advantages of breastfeeding for the mother?
4. What advice do you give to mothers’ partners to help support them breastfeeding?

Related Cases

To Learn More
To view pediatric review articles on thse topics from the past year check PubMed – Breast Milk and
PubMed – Immunization.
Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Breastfeeding, Vaccines and Childhood Vaccines.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Atyeo C, Alter G. The multifaceted roles of breast milk antibodies. Cell. 2021;184(6). doi:10.1016/j.cell.2021.02.031

Perl SH, Uzan-Yulzari A, Klainer H, et al. SARS-CoV-2-Specific Antibodies in Breast Milk After COVID-19 Vaccination of Breastfeeding Women. JAMA. 2021;325(19):2013. doi:10.1001/jama.2021.5782

Kalbermatter C, Fernandez Trigo N, Christensen S, Ganal-Vonarburg SC. Maternal Microbiota, Early Life Colonization and Breast Milk Drive Immune Development in the Newborn. Front Immunol. 2021;12:683022. doi:10.3389/fimmu.2021.683022

Whited N, Cervantes J. Antibodies Against SARS-CoV-2 in Human Breast Milk After Vaccination: A Systematic Review and Meta-Analysis. Breastfeed Med Off J Acad Breastfeed Med. 2022;17(6):475-483. doi:10.1089/bfm.2021.0353

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa