Two new Israeli studies find that COVID-19 antibodies pass robustly from mothers to their infants in breast milk for 6 weeks after vaccination and that no infants breastfed by their coronavirus-positive mothers had evidence of infection.
Strong IgA, IgG antibody transfer
The first study, led by researchers from Shamir Medical Center in Zerifin, Israel, and published as a research letter yesterday in JAMA, involved 504 breast milk samples from a convenience sample of 84 healthcare workers who chose to be vaccinated against COVID-19 because of their occupational risk for COVID-19 infection.
All participants received two doses of the Pfizer/BioNTech coronavirus vaccine 21 days apart and were recruited through ads and social media from throughout Israel from Dec 23, 2020, to Jan 15, 2021. The women provided breast milk samples before they received the vaccine and then once a week for 6 weeks starting 2 weeks after the first dose, and completed weekly questionnaires.
Average levels of SARS-CoV-2–specific immunoglobulin A (IgA) antibodies rose quickly in the breast milk and were significantly elevated 2 weeks after the first vaccine dose. At that time, 61.8% of samples were positive for antibodies, increasing to 86.1% at 4 weeks. Average antibody concentrations stayed high for the rest of follow-up, with 65.7% of samples testing positive at 6 weeks.
Anti-coronavirus immunoglobulin G (IgG) antibodies stayed low for the first 3 weeks after the first dose, increased to 91.7% at 4 weeks, and rose to 97% at 5 or 6 weeks. No mother or baby had serious adverse events over the study period. Mean age of participants was 34 years, and infants were, on average, 10.3 months old.
The authors noted that their findings were similar to those of previous studies showing high COVID-19 antibody concentrations in breast milk, suggesting that breastfeeding would help protect infants against infection.
"This study found robust secretion of SARS-CoV-2 specific IgA and IgG antibodies in breast milk for 6 weeks after vaccination," the researchers wrote. "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)."
The authors also noted some limitations to their study, including a lack of functional antibody testing. "However, previous studies have showed neutralizing capacities of the same antibodies as measured for this study," they wrote. "Second, serum antibody testing or SARS-CoV-2 real-time reverse-transcriptase polymerase chain reaction testing were not performed, which would have provided interesting correlates."
No COVID-19 infections in infants
In the second study, published today in Pediatrics, a team led by researchers from Hadassah-Hebrew University in Jerusalem showed that all 33 newborns of participating women with COVID-19 infections at delivery at 11 Israeli hospitals tested negative for coronavirus from Mar 5 to May 30, 2020. Another 22 infants in the study were not tested for COVID-19, but none had symptoms of coronavirus or were hospitalized within 2 or 3 weeks after they were sent home. One infant died of non-coronavirus causes.
About 95% of the mothers were separated from their newborns at birth for 2 or 3 days because their coronavirus-positive status was known before birth, and their newborns were screened for infection within 48 hours and then again at least 2 weeks after birth. In three cases, the mothers and babies had skin-to-skin contact before the mother's test results came back positive.
The vast majority of women had no or mild COVID-19 symptoms. Two women had pneumonia, and one of them was intubated for a cesarean birth and remained on noninvasive ventilation for several days.
Eighty-nine percent of newborns left the hospital after their mothers were given information on coronavirus infection control. Six newborns were released to households with no COVID-19–positive members, separate from their mothers.
The researchers called the women 14 to 60 days after hospital release to obtain information on breastfeeding and any other infected household members. Forty percent reported at least one other COVID-19–infected household member in addition to the mother.
Of the 55 babies, 74.5% were fed breast milk from the time they were separated at delivery until hospital release, 85% were exclusively breastfed at home, and two were not breastfed.
The authors said that their results can inform public policy regarding neonatal practices in coronavirus-positive mothers.
"With our study results, we suggest that neonates born to SARS-CoV- 2–positive mothers can have an excellent prognosis," the authors concluded.
"With all the neonates testing negative for SARS-CoV-2, ongoing separation after delivery appears unnecessary, as long as careful anti-infection measurements are taken. Furthermore, under these conditions, our study reveals that breastfeeding by a SARS-CoV-2 mother is safe."
Evidence for WHO breastfeeding guidelines
In a commentary on the second study, also in Pediatrics, Genevieve Fouda, MD, PhD, of Duke University; Jesse Kwiek, PhD, of The Ohio State University; and Marcel Yotebieng, MD, MPH, of Albert Einstein College of Medicine, said that the study findings lend more credence to the World Health Organization's recommendation that mothers with confirmed or suspected coronavirus infection be encouraged to start or continue breastfeeding.
But they also noted that maternal antibodies can interfere with the development of immunity in infants after vaccination or infections with certain pathogens. "Whether SARS-CoV-2 maternal antibodies will impact infant response to vaccination remains unknown, and interference will probably depend on the vaccine construct used for infant immunization," they wrote. "Thus, studies to better understand the dynamics of SARS-CoV-2 immune responses in maternal-infant dyads are critically needed."