Preterm infants face increased vulnerability to infectious disease during infancy. This multicenter cohort study sought to evaluate whether breastfeeding up to 6 months of age is associated with reduced incidence of common viral infections during the first year of life in preterm infants.
The primary objective reported was to estimate the effect of breastfeeding exposure through 6 months on the risk of viral infections—specifically influenza, respiratory syncytial (RS) virus, rotavirus, and norovirus—during the first year.
Investigators used data from the Japanese National Hospital Organization Neonatal Intensive Care Unit Registry. The registry contributed data for two time intervals: 2010–2014 and 2016–2018. From that registry, a cohort of preterm infants who completed one-year follow-up was identified.
The analytic sample comprised 3,368 preterm infants with completed follow-up at one year of age. The study was conducted across multiple centers participating in the National Hospital Organization Neonatal Intensive Care Unit Registry in Japan.
Breastfeeding exposure and infection history were obtained using parental questionnaires administered when infants reached one year of age. The exposure of interest was breastfeeding status up to 6 months of age. The source reports that questionnaire responses supplied both feeding exposure information and the documented history of infections occurring in the first year.
The study evaluated the occurrence of four viral infections during the first year of life: influenza virus, respiratory syncytial (RS) virus, rotavirus, and norovirus. These outcomes were based on parental report as captured in the one-year questionnaire.
To test associations between breastfeeding and the risk of each viral infection, investigators used a modified Poisson regression model. The model produced risk ratios (RRs) with corresponding 95% confidence intervals (CIs). Adjusted RRs were reported to account for covariates, although the abstract does not list the specific covariates included in adjustment.
Among 3,368 preterm infants who completed one-year follow-up, breastfeeding up to 6 months of age was associated with a lower risk of influenza infection. The reported adjusted risk ratio for influenza was 0.66 with a 95% CI of 0.48–0.89, indicating a statistically significant reduction in influenza risk among breastfed preterm infants in this cohort.
For other evaluated viral infections (RS virus, rotavirus, norovirus), the authors report a trend toward lower risk with breastfeeding, but the abstract does not provide specific adjusted RRs or confidence intervals for those pathogens. Thus, the presence of an observable trend is reported without detailed effect estimates in the available summary.
The authors interpret their findings to suggest that breastfeeding for up to 6 months may lower the risk of viral infections in preterm infants, with a clear statistically significant association observed for influenza. They suggest that promoting and supporting breastfeeding among families of preterm infants could be one component of infection prevention strategies in this high-risk population.
Given the documented association with influenza and the reported trend for other viruses, the study supports existing public health emphasis on breastfeeding benefits and indicates potential infectious disease prevention value in preterm neonates.
The abstract notes the need for further research to confirm the observed associations and to evaluate the long-term health implications of breastfeeding in preterm infants. Specific limitations implied by the methods include reliance on parental questionnaires for exposure and outcome ascertainment and absence of detail in the abstract on covariates included in adjusted models. The abstract does not report pathogen-specific adjusted estimates for RS virus, rotavirus, or norovirus.
Because the source document presented is an abstract, additional study details—such as the full list of adjusted covariates, definitions of breastfeeding categories, severity or laboratory confirmation of infections, and center-level practices—were not reported in the abstract and therefore are not available here.
The authors report that written informed consent was obtained from parents or legal guardians of all participants at enrollment during the neonatal period. They declare no competing interests. The study appears as an online ahead-of-print article in Pediatric Research with DOI 10.1038/s41390-026-05373-x.
In this multicenter Japanese cohort of 3,368 preterm infants, breastfeeding to 6 months was linked to a lower adjusted risk of influenza in the first year of life (adjusted RR 0.66, 95% CI 0.48–0.89) and showed a possible protective association against other viral infections. The authors recommend breastfeeding support as part of infection prevention efforts for preterm infants and call for further studies to corroborate and extend these findings.