Double blind, randomized, placebo-controlled clinical trial to determine whether supplementation with a probiotic formulation containing 4 probiotic strains (L. plantarum CECT 30292, CECT7484, CECT7485 and P. acidilactici CECT7483) can improve immune response to seasonal influenza vaccination. Subjects with age comprised between 50 and 80 years who meet inclusion and exclusion criteria will be randomized 1:1 to one of the following study groups: one will receive probiotic formulation for 28 days (1 capsule/day) and the other will receive placebo, starting the same day of the influenza vaccination. Main study outcome will be immune response at 4 weeks after vaccination, which will be determined by analysis of specific IgG antibodies in serum against influenza A and B. Secondary outcomes comprise serum titers of specific IgG at 8 weeks after vaccination, percentage of patients with seroconversion at 4 and 8 weeks, evaluation of influenza-like infections or respiratory infections throughout a 4-month period and adverse events.
Randomized clinical trial to determine whether a probiotic formulation containing 4 probiotic strains which belong to Lactiplantibacillus plantarum and Pediococcus acidilactici species can boost the immune response to influenza vaccination evaluated at 4 weeks in a population between 50 and 80 years of age. Secondary outcomes comprise evaluation of immune response at 8 weeks after vaccination, percentage of patients with seroconversion, incidence and duration of influenza-like infections and respiratory infections throughout a 4-month period and safety.