Human milk is the ultimate food to promote healthy growth and development of children aged <2 years.1 Optimal breastfeeding practices, as recommended by the World Health Organization (WHO), include initiation of skin-to-skin contact with breastfeeding within 1 hour of birth, exclusive breastfeeding (EBF) for 6 months, then continued breastfeeding with appropriate complementary foods for up to 2 years and beyond.1 The WHO also recommends that mothers with suspected or confirmed coronavirus disease 2019 (COVID-19) should be encouraged to initiate or continue to breastfeed.2 However, concerns have been raised about whether mothers with COVID-19 can transmit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to their infant or young child through breastfeeding or horizontally.
In a case series of 53 women infected with SARS-CoV-2 and their 55 mostly breastfed infants reported in this issue of Pediatrics, Shlomai et al3 report no neonatal SARS-CoV-2 infections, neither at delivery nor at 2 to 3 weeks postdelivery. The lack of transmission in these mother-infant pairs is consistent with the 9% prevalence of vertical transmission reported in a recent meta-analysis of almost 200 infants.4 Although Shlomai et al3 did not use reverse transcription polymerase chain reaction to screen the breast milk for SARS-CoV-2 RNA, SARS-CoV-2 RNA is uncommon in breastmilk5 and it is unlikely to be transmitted through breast milk. The study by Shlomai et al3 lends further support to the continued breastfeeding of infants born to mothers living with SARS-CoV-2 while respecting infection control measures.
Even if vertical transmission of SARS-CoV-2 rarely occurs, maternal COVID-19 infection can still have an impact on infant health. Notably, maternal antibodies transferred to the infant across the placenta and during the breastfeeding period are critical to protect neonates and young infants from common infections until they are able to mount their own responses. In a few recent studies, researchers have investigated the transplacental transfer of SARS-CoV-2–specific antibodies.6,7 These studies revealed that antibodies against the SARS-CoV-2 spike protein and nucleocapsid are transferred across the placenta, although lower transfer efficiency was observed in women infected with SARS-CoV-2 during the third trimester of gestation compared with women infected earlier in pregnancy. Whereas the levels of anti-spike and anti-nucleocapsid antibodies in cord samples were highly variable and their neutralization potential was not assessed, these results suggest that infants born to SARS-CoV-2–infected women could have some degree of protection. SARS-CoV-2–specific antibodies have also been detected in the breast milk of infected lactating women.8 The fact that none of the infants were infected, despite being surrounded by an ongoing transmission of SARS-CoV-2, suggests that it is possible that these maternally acquired antibodies contributed to the protection of breastfed newborns post discharge in the study by Shlomai et al,3 lending additional support for continued breastfeeding.
However, maternal antibodies can also interfere with the development of infant immunity after infection or vaccination. Notably, it has been revealed that maternal antibody interference contributes to lower the rotavirus vaccine efficacy in low- and middle-income compared with high-income countries.9 In recent studies, researchers have also reported that infants born to women who received a tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed vaccine during pregnancy tend to have lower levels of pertussis-specific antibodies after primary immunization,10,11 suggesting that this phenomenon occurs with live-attenuated vaccines as well as with protein vaccines. 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. Thus, studies to better understand the dynamics of SARS-CoV-2 immune responses in maternal-infant dyads are critically needed.
This large case series lends additional evidence to support the WHO recommendation that mothers with suspected or confirmed COVID-19 should be encouraged to initiate or continue to breastfeed.
Opinions expressed in these commentaries are those of the authors and not necessarily those of the American Academy of Pediatrics or its Committees.
FUNDING: Dr Yotebieng is supported by the following grants from the National Institutes of Health: R01HD087993, U54CA254568, and U01AI096299. The other authors received no external funding. Funded by the National Institutes of Health (NIH).
COMPANION PAPER: A companion to this article can be found online at www.pediatrics.org/cgi/doi/10.1542/peds.2020-010918.
POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.
FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.