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Is breast milk nutrition “alive”, dynamic and impossible to emulate? This question remains important in the context of the emergence of novel diseases and may be answered by comparing it to a few events that happen in nature, with parallels evident in the breast feeding dyad. Edified by nature, and its myriad coexisting species, including the microbes, there seems to be much interplay between species through symbiosis, perhaps, with a lofty purpose. This is compared to the breastfeeding infant’s gut that develops in symbiosis with the microbes that enter it through every feed. Breast milk not only nurtures the infant, but also nourishes the commensal microbes it provides. Milk microbes are influenced by maternal, infant and environmental variables, supporting them differently, parallel to the manner in which microbes and other elements in nature support ecosystems. Reviewing and synthesising information from two different but comparable ecosystems show parallels worthy of appraisal. The lactating mammary gland provides and supports beneficial microbes and microbial environments. Secretory immunoglobulin A (sIgA), the key molecule of mucosal gut immunity, is mutualistic with commensal microbes, capable of mucosal defences, yet preserving equilibrium between pathogen defences and commensal tolerance. Through microbial signals, the nursing mother shares her mucosal immune experiences, commenced in utero, transplacentally and then “translactionally”, to mature infant immunity, concluding an exceptional loop of nurture. Technology allows much appreciation that “immune cross- talk” between mother and infant does occur. In this review, commensal gut microbes in the infant are conceptualised as miniature ecosystems and, breastfeeding, as a vibrant compartment where being “alive” pivots in and around microbial existence and sustenance - a biological setting that, at best, may be emulated but not reproduced.

Background: Immunological protection against novel mucosal pathogens is crucial to us as our immunity is unable to effectively defend against specific pathogens without previous immune encounters, as experienced in the SARS-CoV-2 pandemic. However, a nursing neonate is protected from many novel infections by exclusive human milk feeding despite having a naïve immune system without much previous pathogen exposure. It is observed that SARS-CoV-2 is not transmitted to the nursing infant through human milk and that natural maternal infections produce specific antibody responses in human milk. Furthermore, maternal vaccination against SARS-CoV-2 may modify some of these responses compared to natural infections. In this setting, it was felt necessary to also explore if early, innate immunity in human milk can protect against SARS-CoV-2.To explore this hypothesis, I reviewed the pathogenic mechanisms of COVID-19 focusing on the methods of viral entry through the human mucosae, infection establishment, immune dysregulation, and disease causation, and integrated these with the early actions by human milk feeding on mucosal infections. I then extrapolated the relevant pathways of human milk immune protection as potentials to protect against SARS-CoV-2. Methods: This was divided into three steps which firstly included a literature search, secondly a stepwise analysis and synthesis of data, and thirdly, an integration of data to form a hypothesis. The first step searched articles in two areas. In the first area, articles included were on the infection and pathogenesis of SARS-CoV-2, and in the second area, articles included were on innate immunity in human milk. In the second step, I analyzed the immunological actions in human milk against mucosal infections, on the whole, and synthesized some of these relevant actions against the pathogenesis of SARS-CoV-2 infections. In the third step, I integrated human milk immune pathways that could interfere with the establishment of SARS-CoV-2 infection, viral invasion, immune dysregulation, and the progression of the disease. Results: Infection by SARS-CoV-2 can theoretically be reduced or mitigated by the effect of early immune constituents in human milk. Human milk feeding may confer protection against all stages of the disease including the establishment of SARS-CoV-2 infection, invasion, and immune dysregulation and these actions may benefit both the individual and the community. Limitations: The multifunctional and dynamic nature in which human milk constituents function in a nursing infant cannot be fully reproduced by studying isolated components under experimental conditions. Even when such factors can theoretically offer protection against the virus, this concept has to be further researched in large cohorts of nursing infants. Conclusion: The role of human milk in preventing infection by SARS-CoV-2 must be explored further and if true, exclusive human milk feeding must be considered another reason for the smaller number of infections observed in children compared to adults in the pandemic. The additional counseling of human milk feeding for protection against novel pathogens, besides its established role in reducing neonatal mortality, would enhance rates of exclusive human milk feeding. General health can be developed and promoted through the potential immunotherapy provided by it.