A comprehensive trial in New Zealand concludes that daily oral probiotic Streptococcus salivarius K12 from infancy does not reduce the risk of ear infections, respiratory illnesses, or antibiotic use in children up to two years old.
A daily oral probiotic given from infancy to the age of two did not lower the risk of ear infections, respiratory infections or antibiotic use in a large New Zealand trial, according to findings published in the European Journal of Pediatrics. The study tested Streptococcus salivarius K12, a strain sometimes marketed for mouth and throat health, in healthy infants aged three to six months.
Researchers enrolled 428 babies in Wellington and Christchurch and randomly assigned them to receive either the probiotic or a matching placebo from six months until 24 months of age. The main measure was doctor-recorded acute otitis media, or ear infection, over the 18-month treatment period. Secondary measures included visits for respiratory tract infections, antibiotic prescriptions, croup and the severity of ear disease.
The trial found no meaningful difference between the two groups. Ear infections were recorded in 37.23% of children given the probiotic, compared with 38.89% in the placebo group. Rates of respiratory illness, antibiotic prescribing and parent-reported serious adverse events were also similar. The authors said the results do not support routine use of S. salivarius K12 to prevent ear or respiratory infections in the general infant population.
The findings add to a mixed evidence base. A systematic review published in April 2026 said studies of S. salivarius K12 have remained heterogeneous and inconclusive, with more research needed to clarify whether it can prevent upper respiratory infections or acute otitis media. Earlier laboratory and small clinical studies had suggested possible benefit, including in vitro work showing inhibition of some otitis media pathogens and preliminary trials reporting fewer recurrent infections, but later pragmatic research in schoolchildren also failed to show a clear preventive effect.
The new study had some limits. Follow-up overlapped with Covid public health restrictions in New Zealand, which likely changed the circulation of respiratory viruses and patterns of healthcare use. General practice data were unavailable for a minority of participants, and adherence declined over time. Even so, the authors said their results, taken alongside existing placebo-controlled evidence, do not justify routine use of the probiotic for prevention in young children.
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