In the largest study of UK infant microbiomes to date researchers from UCL and the Wellcome Sanger Institute discovered that babies with a specific gut bacteria mix at just one week old were less likely to be hospitalized for viral lower respiratory tract infections (vLRTIs) within their first two years.

This protective microbiome profile was only observed in some infants born via vaginal delivery.

Expanding on earlier results from the UK Baby Biome Study the new findings suggest that specific gut microbiome profiles may offer benefits such as protection against viral infections.

While more research is needed to confirm this connection the study paves the way for future efforts in preventing childhood respiratory illnesses potentially through targeted probiotics designed to lower infection risks in infants.

Lead author Dr. Cristina Garcia-Mauriño stated: Viral lower respiratory tract infections are a major cause of hospitalisation in young children and our findings suggest that early gut microbiome composition could reduce this risk.

Further investigation is needed to understand these mechanisms including the possible interaction between the gut and lung microbiomes which could inform new strategies to prevent respiratory infections in early life.

The gut microbiome a vital ecosystem for immune development begins forming at birth making the first month a key window for intervention. UCL researchers previously found differences in microbiomes based on birth mode with variations leveling out by age one. They also identified three types of pioneer bacteria in UK newborns with B. longum and B. breve offering beneficial effects. In the latest study babies born vaginally with higher levels of B. longum and other beneficial species had a lower risk of hospitalisation for vLRTIs.

Even after accounting for factors like antibiotic use and feeding method the link between certain gut microbiomes and reduced vLRTI risk remained.
Interestingly not all vaginally born babies shared this protective microbiome some had profiles similar to those born via C-section with comparable hospitalisation risks.The study highlights an association not causation between early gut bacteria like B. longum and reduced infection risk with future research needed to explore broader health impacts.
Researchers hope the upcoming 4M study will uncover how early microbiomes influence long-term health and pave the way for targeted, personalized infant probiotics.

Source: https://www.ucl.ac.uk/news/2025/jun/babys-microbiome-protects-against-childhood-viral-infection