Infant health · November 4, 2026
Four weeks of probiotic drops from birth, and 638 days of diarrhoea against 1,057 in 1,945 Tanzanian babies. Whether fewer babies fell ill is less clear
Most first bouts came months after the last drop. Babies on the probiotic ran up about 40% fewer diarrhoea days and fewer long illnesses, but neither the number who got sick nor how long a typical bout lasted cleared the statistical bar, and the same trial had already found no effect on hospital stays or deaths.
Around Haydom, in rural northern Tanzania, many families draw untreated water from boreholes, shallow wells or the surface, and handwashing stations often have no soap. Researchers from Tanzania and Norway asked whether a few drops a day in the first month of life could leave a baby better protected in that setting. Their new analysis of the ProRIDE trial, published in BMJ Paediatrics Open on 31 October, looks at diarrhoea up to six months of age.
The trial enrolled 2,000 healthy newborns weighing at least 2 kg, born in hospital, at local health facilities or at home, between February 2022 and January 2023. Half got five drops a day of a mix of three bacterial strains, one Lactobacillus and two Bifidobacterium, 2 billion colony-forming units in all. The other half got a placebo. Caregivers gave the drops at home for four weeks, and neither they nor the staff knew which was which. Data at six months were available for 1,945 babies, and 90% of caregivers reported giving the drops daily.
Diarrhoea, defined by the WHO standard of three or more loose stools in 24 hours, hit 53 of 970 babies on the probiotic (5.5%) and 73 of 975 on placebo (7.5%). That gap didn't reach significance (P = .070). Total days of diarrhoea did, narrowly: 638 against 1,057 (P = .048), which is about 40% fewer by our division. Illness lasting more than 14 days affected 7 of the 53 sick babies on probiotic (13%) and 21 of the 73 on placebo (29%; P = .038).
Those are the figures that stand out, so it helps to take them apart. A total is the number of sick babies multiplied by how long each stayed sick, and neither piece was clearly different by itself. The median illness lasted 7 days on probiotic and 9 on placebo (P = .091). The 13% and 29% are shares of babies who already had diarrhoea; counted across everyone in each group, they come to about 7 and 22 per 1,000 (our division), and that rests on 28 babies in all. Illnesses were also mostly mild: none met the WHO criteria for severe dehydration, none of the babies with diarrhoea died, and 2 were admitted to hospital, both from the probiotic group, too few to read anything into. Clinic visits for diarrhoea were similar as well (30% and 36% of the sick babies).
Timing makes the result more curious. The median first bout came at 157 days old, around four months after the drops stopped (our sum). Stool samples taken at six weeks, a median 123 days before illness in the 100 babies analysed, showed 24 bacterial species differing in abundance from 235 matched babies who stayed well, with more potentially harmful gut bacteria and fewer lactic acid producers among those who later got sick. Yet the overall make-up of the gut community didn't differ between them (P = .385). The drops did shift that community (P = .001), but sorting babies into high and low Bifidobacterium groups didn't predict who got diarrhoea (P = .51). So the probiotic clearly changed the gut, and this study can't show that the change is what protected anyone.
The limits are substantial. This is a post hoc analysis, and the trial's main question had already been answered in 2025: hospitalisation or death in the first six months came to 34 of 970 on probiotic and 31 of 975 on placebo, with no difference (relative risk 1.10, 95% CI 0.68 to 1.78). Diarrhoea reports came from caregivers rather than clinicians. With P values of .048 and .038 among several comparisons, and no correction for multiple testing described for these clinical results, chance is a live explanation. Few babies got diarrhoea, and follow-up stopped at six months, before the 6-to-24-month period when it peaks. Every baby with data was still breastfed at six weeks and about 80% at six months, about 90% had rotavirus vaccine, and the authors caution that the results may not apply to other settings or to preterm babies. They treat it as grounds for further trials. Funding came from Norwegian health authorities and research funders with no role in the study, and the authors declared no competing interests.
Newborn probiotic drops and diarrhoea to six months in rural Tanzania: post hoc analysis of the ProRIDE randomised trial (BMJ Paediatrics Open, 31 October 2026)
2,000 / 1,945
Newborns randomised, and those with six-month data for this analysis
5.5% vs 7.5%
Babies with diarrhoea, probiotic vs placebo: 53 of 970 and 73 of 975 (P = .070, not significant)
638 vs 1,057
Total days of diarrhoea across each group (P = .048): about 40% fewer, by our division
7 vs 9 days
Median length of illness among babies who got diarrhoea (P = .091, not significant)
13% vs 29%
Sick babies whose diarrhoea lasted over 14 days: 7 of 53 and 21 of 73 (P = .038)
7 vs 22 per 1,000
The same 7 and 21 babies as a share of everyone in each group (our division)
157 days
Median age at first bout of diarrhoea; drops were given only for the first 4 weeks
34 vs 31
Hospitalisation or death to six months, the trial's main outcome: relative risk 1.10 (95% CI 0.68 to 1.78), no difference
This analysis was post hoc, so the P values are exploratory. Diarrhoea was reported by caregivers and checked against the WHO definition; reports lacking enough detail were excluded. The per-1,000 figures, the 40% and the 'about four months' are our own arithmetic from the paper's counts, not the authors'. The paper gives the interquartile range for age at first bout as 89 to 169 days in its text and 95 to 169 in Table 2. The methods name the tests for median duration and proportions but don't spell out how the two total-days figures were compared.
- The totals work out at about 12 diarrhoea days per sick baby on probiotic and 14.5 on placebo (our division). The medians, 7 and 9, are lower, a sign that a few long illnesses pull the totals up.
- Antibiotic use by six months was far higher in babies who had diarrhoea (55% against 17%), but the authors warn it may reflect treatment of the illness rather than a cause of it.
- Lacticaseibacillus rhamnosus, a species often used as a probiotic, was among the bacteria scarcer in babies who later got diarrhoea. It wasn't one of the three strains in these drops.
- The paper puts diarrhoea deaths in low- and middle-income countries at more than 444,000 a year, with over 60% in babies under 12 months.
- The researchers could check the drops were really given: stool sequencing showed more Bifidobacterium in the probiotic group, backing up what caregivers said.
- Probiotics and diarrhoea morbidity among infants in Tanzania: secondary analysis of a randomised clinical trialBMJ Paediatrics Open, 31 October 2026 · Open access (CC BY-NC 4.0). Abstract, methods, Tables 1 and 2, figures, discussion, limitations, funding and competing interests.
- Full text of the paperPubMed Central · Free copy of the same article, used to check the figures.
- Home administration of a multistrain probiotic once per day for 4 weeks to newborn infants in Tanzania (ProRIDE)The Lancet Global Health, June 2025 · The main trial report: hospitalisation or death to six months, and dosing details.
- ProRIDE trial registration, NCT04172012ClinicalTrials.gov · Registry entry for the trial.
- Newborn baby feetWikimedia Commons · CC0 image by Janko Ferlič.
General information, not medical advice. This analysis looks at healthy newborns in one rural part of Tanzania and doesn't show that babies elsewhere should be given probiotics. Speak to your paediatrician before giving your baby any supplement, particularly if your baby was born early or is unwell. If a baby has diarrhoea and feeds poorly or shows signs of dehydration such as few wet nappies, get medical help promptly.
Analysis by NutroPractic from the sources listed. Written for general readers; it does not replace advice from your own doctor.
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