Probiotics are live, friendly bacteria that can help keep us healthy when taken in the right amounts. Most probiotics belong to groups of bacteria that are naturally found in the body, especially in the digestive system. They help keep a healthy balance of bacteria in the stomach, support digestion, and may even lower the risk of some illnesses.

One type of these good bacteria is common in the human stomach and intestines, but their numbers tend to go down as we get older. In babies who are breastfed, these helpful bacteria are usually the most common ones in their stomachs during the first few weeks of life.

Recent studies have shown that changes in the mix of bacteria living in the stomach and intestines are closely linked to a higher risk of gut diseases and malnutrition in young children. In healthy babies, the stomach and intestines are usually full of helpful bacteria like Lactobacillus and Bifidobacterium, which support important body functions for growth like building a strong immune system, helping the body process food like breastmilk, and protecting against harmful germs. When there’s an imbalance in these stomach bacteria, where harmful types grow too much and the helpful ones are fewer, this can cause long-term problems in how the body works and fights off illness. This is especially true for children who are malnourished.

Being underweight puts children at very high risk, especially in poorer countries. Every year, more than 3 million children die because they don’t get enough nutrition. This makes up nearly half of all deaths in children under 5 years old. Babies who are already underweight and then get sick in the hospital are even more likely to die. Similar death rates have been seen in studies of malnourished children both during hospitalization and after discharge. An imbalance in these good bacteria in the body is thought to cause poor digestion of food leading to babies who are smaller or lighter than expected for their age.

Current treatments for babies help them grow by giving the nutrients they need, but they don’t fix problems in the gut bacteria. Healthy stomach bacteria are important because they help digest food, absorb nutrients, and stop harmful germs from multiplying and spreading.

The study will be conducted at several sites, with KEMRI CRDR being one of the selected sites.  The target overall global sample size will be 400 infants, with KEMRI-CRDR targeting at least 20-30 participants.

The primary objective of the study will be to evaluate the change in weight of infants receiving Bifin02 and LGG®.

Screening will be done while the infant is still in the hospital, within a week before they are expected to go home. After explaining the study to the parent or legal guardian and obtaining informed consent, infants aged 30 to 120 days who qualify will be randomly assigned to the study. Each child will participate in the study for three months.

Consent will be explained in detail to the parent or legal guardian (preferably the mother), who will then sign to confirm their agreement before enrolment. Only eligible infants will be enrolled.

Infants will be randomly placed in two groups, not in any order, but equal numbers and any infant has a chance to be in either group.  One group will be given the product being studied  Bifin02 with LGG® and the other group will be given a product that looks like the one being studied but not containing the product being studied ( placebo). The study product (Bifin02 with LGG® or placebo) will be given once daily for 28 days. It will be provided as a powder that the mother mixes with about 10 mL of breastmilk and given to the baby by a feeding syringe. If breastmilk is not available, the powder can be mixed with about 10 mL of clean water.

Follow-up will include both home visits (at weeks 1, 2, 3, 5, 6, and 7) and clinic visits (at months 1, 2, and 3). During these visits, the team will check the baby’s health and look out for any side effects. Blood and stool samples will be collected at the start of the study, at month 1, and at month 2 (stool only).

The results of the research will be shared with national and international paediatric and infectious disease conferences, healthcare workers at the study sites, and the community advisory board.

Malnutrition in infants remains a major health challenge in low- and middle-income countries (LMICs), where undernutrition is often exacerbated by gut dysbiosis, an imbalance in intestinal microbiota that impairs nutrient absorption, immune development, and resistance to enteric pathogens. A healthy infant gut is typically dominated by Bifidobacterium (Bifin02) and Lactobacillus, which support digestion, metabolism, and immune maturation. Bifidobacterium infantis plays a key role in breaking down and absorbing human milk oligosaccharides (HMOs), and supplementation with strain EVC001 improves gut colonization, microbiome composition, and reduces pro-inflammatory cytokines. Lactobacillus rhamnosus GG (LGG®) is widely recommended for managing acute gastroenteritis and preventing antibiotic-associated and nosocomial diarrhoea, with evidence of benefit in undernourished children. Current therapies for underweight infants primarily deliver nutrients but do not correct underlying microbial imbalances critical for digestion and pathogen control. This Phase 3, randomized, double-blind, placebo-controlled trial will evaluate whether co-administration of Bifin02 and LGG® improves weight gain and is safe in underweight infants (−4.5 ≤ WAZ < −2.0) aged 1–4 months recently discharged after acute non-surgical illness. A total of 400 participants will be enrolled across Kenya and Zimbabwe, with at least 100 recruited from Kenya and 20–30 from the Kenya Medical Research Institute- Center for Respiratory Disease Research (KEMRI-CRDR) site. Kenyan recruitment sites include Mama Lucy Hospital and St. Francis Hospital (inpatient), and Riruta Hospital, Mama Margaret Uhuru Hospital, Mathare North Hospital, Chandaria Hospital, Kayole 2 Hospital, and Dandora 2 Hospital (outpatient), alongside participating centres at KEMRI Mtwapa in Mombasa and Moi University Clinical Research Center in Eldoret. The Zimbabwe site (Mutala Research Site) will recruit from Parirenyatwa Group of Hospitals, Sally Mugabe Central Hospital, and Chitungwiza Central Hospital. If effective, Bifin02 and LGG® may offer a safe, microbiome-directed dietary intervention to support growth and reduce disease vulnerability in underweight infants in LMICs