Hao et al., Cochrane Database of Systematic Reviews,
doi:10.1002/14651858.CD006895.pub3 (Preprint) (meta analysis)
Probiotics for preventing acute upper respiratory tract infections
Meta analysis of 12 RCTs with 3,720 patients showing probiotics reduced acute upper respiratory tract infections.
Hao et al., 1/1/2015, preprint, 3 authors.