Polyvalent mechanical bacterial lysate (PMBL) is used for the treatment and prevention of recurrent respiratory tract infections. Although PMBL is an immunostimulant, it remains unknown whether treatment with PMBL influences natural killer cell activity (NKA). Hence, this case-control study compared the changes in IFN-γ levels (surrogate index for NKA) following PMBL treatment or time passing between the PMBL-treated group and controls. The treatment group included adults who had a PMBL prescription for three months against recurrent respiratory tract infection from an outpatient clinic, while the control group had healthy adults visiting the health promotion center for periodic health check-ups. The control group (N = 506) showed no change in IFN-γ levels, while the treatment group (N = 301) showed a significant increase in mean from 462.8 to 749.3 pg/mL after PMBL treatment. In the subgroup with IFN-γ <500 pg/mL, IFN-γ levels significantly increased in both groups. However, the change in the treatment group (287 ± 822 pg/mL) was greater than that in the control group (58 ± 809 pg/mL), and the interaction between the visit and case/control was significant (p = 0.030) in a generalized estimating equation model. In conclusion, NKA increased in the subjects with recurrent respiratory tract infections with PMBL treatment.

Over many years, OM-85, a lysate of 21 common bacterial respiratory pathogens, has been demonstrated to prevent respiratory recurrences in children. However, further studies are needed to explore the true importance of OM-85 in the prevention of respiratory tract infections (RTIs) in children. This study was planned to further contribute to the evaluation of the role played by OM-85 in prevention of recurrent RTIs in children.
This study was a randomized (3:3:1), placebo-controlled, double-blind, single-centre, phase IV trial carried out in Italy to assess the efficacy of OM-85 (Broncho-Vaxom®; Vifor Pharma; Meyrin 2/Geneva, Switzerland) in reducing the number of new RTI episodes in 288 children aged 1 to 6 years with a history of recurrent RTIs and to compare the efficacy of the standard 3-month regimen with that of administration of OM-85 for 6 months during a 6-month study period.
The number of RTIs and of children who experienced at least one RTI were significantly lower among patients receiving OM-85 for 3 months than among those given placebo (33% vs 65.1%, p < 0.0001). Differences were statistically significant for upper RTIs (i.e., common cold/viral pharyngitis and acute otitis media; p < 0.0001 and p = 0.006, respectively). Days of absence from day-care for children and working days lost by parents were significantly lower in the group with children treated with OM-85 for 3 months than in the placebo group (p = 0.007 and p = 0.004, respectively). No difference was seen between children who received OM-85 for 3 and those who received OM-85 for 6 months. The prevalence of atopy as well as the history of recurrent wheezing and age of the study child did not influence the results. Benefit was maximally evident among children with a history of frequent recurrences. OM-85 was well tolerated and safe, even in children who received an influenza vaccination.
The use of OM-85 for 3 months in 3 series of 10 consecutive days each time reduces the risk of recurrent RTIs in children, with a favourable safety profile. The greater effect observed in children prone to several respiratory episodes than in non-prone children seems to indicate that this lysate should be administered especially to children with a proven high susceptibility to RTIs.