The Bloom Infant Probiotic (BIP) Study

The goal of this clinical trial is to investigate whether administering a probiotic (Infloran®) to infants who received antibiotics in the first 28 days of life can restore or enhance their immune response to routine vaccines. Antibiotic use in the first weeks of life can lower the levels of beneficial gut bacteria, such as bifidobacteria, which play a key role in immune function. As a result, infants treated with antibiotics may produce fewer antibodies after routine vaccinations, leaving them less protected against infections. The main questions this study aims to answer are: * Does treatment with the probiotic Infloran® improve the geometric mean concentrations (GMCs) of anticapsular antibodies against at least 11 serotypes included in the pneumococcal conjugate vaccine (PCV20) in serum samples collected at 6 months of age compared with placebo in infants treated with antibiotics in the neonatal period? * Does treatment with the probiotic Infloran® improve the GMCs for the pneumococcal conjugate vaccine (PCV20) at 12 months of age compared with placebo in infants treated with antibiotics in the neonatal period? * Does treatment with the probiotic Infloran® improve the GMCs of other routine childhood vaccines at 6 and 12 months of age compared with placebo in infants treated with antibiotics in the neonatal period? * Does treatment with the probiotic Infloran® increase the proportion of infants achieving seroprotective antibody levels for pneumococcal antigens compared to placebo in infants treated with antibiotics in the neonatal period? * What are the differences in antigen specific T cell responses, flow cytometry, blood transcriptomics, and gut microbiota composition in the probiotic (Infloran®) vs placebo groups in infants treated with antibiotics in the neonatal period? Researchers will compare infants who receive Infloran® (a probiotic containing Bifidobacterium bifidum and Lactobacillus acidphilus) with those who receive a placebo (which contains the s