Oral intake of Lactobacillus fermentum CECT5716 enhances the effects of influenza vaccination

Objective We studied the coadjuvant capability of oral consumption of the breast-milk–isolated strain Lactobacillus fermentum (CECT5716) for an anti-influenza vaccine. Methods A randomized, double-blinded, placebo-controlled human clinical trial including 50 volunteers (31 male and 19 female) was performed to address the immunologic effects of an intramuscular anti-influenza vaccine in adults (33.0 ± 7.7 y old). Fifty percent of volunteers received an oral daily dose of methylcellulose (placebo) or probiotic bacteria (1 × 1010 colony-forming units/d) 2 wk before vaccination and 2 wk after vaccination. Results Two weeks after vaccination there was an increase in the proportion of natural killer cells in the probiotic group but not in the placebo group. The vaccination induced an increase in T-helper type 1 cytokine concentrations and in T-helper and T-cytotoxic proportions in both groups; however, the probiotic group showed a significant higher induction in some of these parameters. Regarding the humoral effects, induction of antibody response in the placebo group could not be detected. In the case of the probiotic group, a significant increase in antigen specific immunoglobulin A was detected. Although an increase in total immunoglobulin M was observed, changes in anti-influenza antigen specific immunoglobulin M were not observed. The incidence of an influenza-like illness during 5 mo after vaccination (October to February) was lower in the group consuming the probiotic bacteria. Conclusion Oral administration of the strain L. fermentum CECT5716 potentates the immunologic response of an anti-influenza vaccine and may provide enhanced systemic protection from infection by increasing the T-helper type 1 response and virus-neutralizing antibodies.