Preterm infants may face a heightened risk of viral infection during the first year of life, when the immune system is still developing and the protective barriers of the lungs and intestine remain immature. A multicenter cohort study led by Y. Kamiya, A. Takeuchi and K. Nakamura has examined whether breastfeeding through the first six months is associated with the incidence of viral infections in these medically vulnerable infants. Published in Pediatric Research, the study focuses on an important question in neonatal medicine: whether the type and duration of early feeding may influence exposure to, or the clinical consequences of, common viruses during infancy. The research does not treat breastfeeding as a simple nutritional choice, but as a possible component of early immune protection.
Prematurity can alter nearly every stage of host defence. Infants born before term may have lower concentrations of maternally transferred immunoglobulin G, because a substantial proportion of placental antibody transfer occurs late in pregnancy. Their skin and mucosal surfaces are also less mature, while their respiratory systems are more susceptible to inflammation and impaired clearance of pathogens. In addition, many preterm infants require prolonged hospital care, respiratory support or repeated medical procedures, all of which can increase opportunities for exposure to infectious agents. Viral illnesses that are relatively mild in older children can therefore cause bronchiolitis, pneumonia, feeding difficulty, dehydration or prolonged hospitalisation in infants born prematurely.
Breast milk contains more than calories, proteins and fats. It is a complex biological fluid carrying antibodies, immune cells, cytokines, oligosaccharides, antimicrobial proteins and molecules that help regulate inflammation. Secretory immunoglobulin A, or sIgA, is particularly important at mucosal surfaces. Rather than circulating primarily through the bloodstream, sIgA can bind pathogens in the mouth, throat and gastrointestinal tract, limiting their attachment to epithelial cells and reducing the likelihood that viruses will cross the mucosal barrier. Human milk oligosaccharides can also act as decoys for microbes and support beneficial bacterial communities in the intestine, potentially influencing the development of systemic and mucosal immunity.
The study’s central exposure is breastfeeding status up to six months of age, a period that includes major changes in infant feeding and immune maturation. In a cohort design, researchers follow a defined group of infants over time and compare health outcomes according to an exposure measured during the study period. Here, the outcome of interest is the incidence of viral infections during the first year of life. This approach is useful because it can capture infections as they occur rather than relying entirely on parental recall after the fact. It may also allow investigators to examine whether an association persists beyond the immediate neonatal period, when breastfeeding and hospital-based care are closely intertwined.
The relationship between breastfeeding and infection is biologically plausible but scientifically difficult to interpret. Infants who receive breast milk may differ from those who do not in many ways unrelated to milk itself. Maternal health, socioeconomic conditions, access to lactation support, mode of delivery, household crowding, exposure to siblings, vaccination, smoking exposure and the severity of the infant’s prematurity can all affect infection risk. The need for neonatal intensive care may influence both the ability to breastfeed and the likelihood of encountering respiratory viruses. For this reason, a multicenter cohort can be valuable: data collected across different hospitals and clinical settings may provide a broader picture than a single-unit study, although observational research cannot by itself prove that breastfeeding directly prevents infection.
The investigators’ focus on viral infections is especially relevant because viruses remain a major cause of respiratory and gastrointestinal illness in the first year of life. Respiratory syncytial virus, influenza, rhinoviruses, adenoviruses, human metapneumovirus and other respiratory pathogens can be consequential for preterm infants, whose smaller airways and limited pulmonary reserve may magnify the effects of inflammation and mucus production. Gastrointestinal viruses can be equally disruptive, particularly when vomiting or diarrhoea compromises hydration and nutritional recovery. The biological effects of breast milk may differ according to the virus, the route of exposure and whether protection occurs through direct neutralisation, altered microbial ecology or modulation of the infant’s inflammatory response.
A key scientific issue is how breastfeeding status is defined. “Breastfeeding” can refer to exclusive breastfeeding, predominant breastfeeding, any breast milk intake or a combination of breast milk and formula. These categories may have different biological implications. The volume and duration of milk exposure may also matter, as may whether the infant receives fresh milk, expressed milk or donor milk. For preterm infants, feeding is often interrupted by medical instability, and some infants transition gradually from tube feeding to oral feeding. A careful analysis therefore needs to distinguish the timing and continuity of breast-milk exposure from the broader clinical circumstances surrounding birth and hospital discharge. The study’s stated six-month window highlights the importance of these details in evaluating longer-term associations.
The findings from this research may help clinicians refine infection-prevention counselling for families of preterm infants, but they should be interpreted within the limits of the evidence reported. The available study description identifies the objective and design but does not provide numerical results, infection-specific estimates or conclusions about causality. It therefore cannot support a claim that breastfeeding eliminates viral infections or that every preterm infant who receives breast milk will experience fewer illnesses. Breastfeeding support must remain individualised, respectful and medically appropriate, particularly when mothers face illness, medication use, low milk production, psychological stress or barriers to expressing milk. When direct breastfeeding is not possible, expressed maternal milk may still provide many of the same biological components, while donor milk and specialised formulas may be clinically necessary alternatives.
By examining viral infections across the first year rather than only during the neonatal admission, the multicenter cohort study places breastfeeding within the broader timeline of infant immune development. Protection in early life is rarely determined by one factor. Maternal antibodies, vaccination, infection-control practices, ventilation, hand hygiene, household exposure and timely medical care all contribute to risk. Breast milk may form one layer in this defence system, supplying locally active antibodies and immune-regulating compounds during a period when the infant’s own responses are still being calibrated. The significance of the work lies in testing that possibility in preterm infants, a group for whom even modest reductions in viral illness could have meaningful consequences for respiratory health, growth and hospital use. Further studies, including analyses that clarify viral species, feeding intensity and potential confounding factors, will be needed to determine how strongly breastfeeding status predicts infection and which mechanisms are most important.
Subject of Research: Breastfeeding and viral infections in preterm infants
Article Title: Breastfeeding and viral infections in preterm infants: a multicenter cohort study
Article References: Kamiya, Y., Takeuchi, A., Nakamura, K. et al. Breastfeeding and viral infections in preterm infants: a multicenter cohort study. Pediatric Research (2026). https://doi.org/10.1038/s41390-026-05373-x
Image Credits: AI Generated
DOI: 10.1038/s41390-026-05373-x
Keywords: breastfeeding, preterm infants, viral infections, infant immunity, human milk, respiratory infections, multicenter cohort study, neonatal health
