Effects of Lactobacillus coryniformis K8 CECT5711 on the immune response to influenza vaccination and the assessment of common respiratory symptoms in elderly subjects: a randomized controlled trial

PURPOSE: Elderly people are particularly vulnerable to seasonal influenza. Therefore, vaccination is strongly recommended. However, the vaccine efficacy is lower in the elderly, owing to immunosenescence. The objective of the present study was to evaluate the ability of the probiotic strain Lactobacillus coryniformis K8 CECT5711 to enhance the immune response to the influenza vaccine in the elderly and to assess the effects on symptoms related to respiratory infections. METHODS: A randomized, double-blind, placebo-controlled trial was conducted between November 2015 and April 2016. A total of 98 nursing home residents, more than 65 years of age were randomly assigned to receive L. coryniformis K8 CECT5711 (3 × 10(9) CFU/day) or a placebo for 2 weeks before influenza vaccination. The primary outcome was the percentage of seroconversion. The secondary outcomes were the incidence of influenza-like illness (ILI) and respiratory symptoms associated with respiratory infections during the 5-month follow-up period. The serum cytokine and immunoglobulin levels were also evaluated. RESULTS: The percentage of responders to vaccination was higher in the probiotic group than in the control group (p = 0.036). L. coryniformis ingestion was associated with a significantly lower incidence of respiratory symptoms commonly associated with respiratory infections (p = 0.007) and lower consumption of analgesics (p = 0.008). CONCLUSION: The administration of L. coryniformis K8 CECT5711 to an elderly population increased the immune response against the influenza vaccine and decreased symptoms associated with respiratory infections. Probiotic administration may be a natural and safe strategy to improve the efficacy of vaccines and to protect against common respiratory infections in susceptible populations.