The breast milk of women who had received Pfizer’s COVID-19 vaccine contained specific antibodies against the infectious disease, new research found.
“The COVID-19 pandemic has raised questions among individuals who are breastfeeding, both because of the possibility of viral transmission to infants during breastfeeding and, more recently, of the potential risks and benefits of vaccination in this specific population,” researchers wrote.
In August, the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, and most recently, the Centers for Disease Control and Prevention, recommended that pregnant people receive the COVID-19 vaccine.
The study, published Aug. 11 in JAMA Network Open, adds to a growing collection of research that has found COVID-19 antibodies in the breast milk of women who were vaccinated against or have been infected with the illness.
Study author Erika Esteve-Palau, MD, PhD, and her colleagues collected blood and milk samples from 33 people who were on average 37 years old and who were on average 17.5 months post partum to examine the correlation of the levels of immunoglobulin G antibodies against the spike protein (S1 subunit) and against the nucleocapsid (NC) of SARS-CoV-2.
Blood and milk samples were taken from each study participant at three time points – 2 weeks after receiving the first dose of the vaccine, 2 weeks after receiving the second dose, and 4 weeks after the second dose. No participants had confirmed SARS-CoV-2 infection prior to vaccination or during the study period.
Researchers found that, after the second dose of the vaccine, IgG(S1) levels in breast milk increased and were positively associated with corresponding levels in the blood samples. The median range of IgG(S1) levels for serum-milk pairs at each time point were 519 to 1 arbitrary units (AU) per mL 2 weeks after receiving the first dose of the vaccine, 8,644 to 78 AU/mL 2 weeks after receiving the second dose, and 12,478 to 50.4 AU/mL 4 weeks after receiving the second dose.
Lisette D. Tanner, MD, MPH, FACOG, who was not involved in the study, said she was not surprised by the findings as previous studies have shown the passage of antibodies in breast milk in vaccinated women. One 2021 study published in JAMA found SARS-CoV-2–specific IgA and IgG antibodies in breast milk for 6 weeks after vaccination. IgA secretion was evident as early as 2 weeks after vaccination followed by a spike in IgG after 4 weeks (a week after the second vaccine). Meanwhile, another 2021 study published in mBio found that breast milk produced by parents with COVID-19 is a source of SARS-CoV-2 IgA and IgG antibodies and can neutralize COVID-19 activity.
“While the data from this and other studies is promising in regards to the passage of antibodies, it is currently unclear what the long-term effects for children will be,” said Dr. Tanner of the department of gynecology and obstetrics at Emory University, Atlanta. “It is not yet known what level of antibodies is necessary to convey protection to either neonates or children. This is an active area of investigation at multiple institutions.”
Dr. Tanner said she wished the study “evaluated neonatal cord blood or serum levels to better understand the immune response mounted by the children of women who received vaccination.”
Researchers of the current study said larger prospective studies are needed to confirm the safety of SARS-CoV-2 vaccination in individuals who are breastfeeding and further assess the association of vaccination with infants’ health and SARS-CoV-2–specific immunity.
Dr. Palau and Dr. Tanner had no relevant financial disclosures.