Effect of a Multi-strain Probiotic Formulation on Immune Response to Influenza Vaccination

Inclusion Criteria: * Subjects 50 - 80 years old receiving seasonal Influenza vaccine in season 2021-2022 * Body mass index (BMI) 18.5-34.9 kg/m2 * Willing to provide informed consent * Able to follow study procedures, according to the criteria of study investigator Exclusion Criteria: * Hypersensitivity to any of the components of influenza vaccine * Previous influenza infection in the same season (from 01/09/2021) * Having received influenza vaccination in the previous season less than 9 months before study entry (from 01/01/2021) * Having received another vaccine -different from COVID19 vaccine- up to 1 month before study inclusion or planning to receive it 1 month after study inclusion * Active infection at the moment of study entry as diagnosed by study physician * History of severe allergic reactions (food and non-food), including severe asthma. * Receiving immunosuppressant therapy, displaying neutropenia, lymphopenia, AIDS, immunoglobulin deficiency, active oncological disease. * Daily ingestion of any food complement or food added with probiotics (including Actimel o similar products) 2 weeks before inclusion in the study * Acute pancreatitis, short bowel syndrome or active inflammatory bowel disease * Diagnosed from other pathologies that according to study physician may compromise the immunological function of the individual (such as immunodeficiencies, lupus, multiple sclerosis, among others) * Having received antibiotic treatment in the previous month Exclusion criteria during the study: * Withdrawal from the study as per study investigator criteria, in case that study procedures are not followed by the participant * In case of adverse event that prevents them from following study procedures or complying with the treatments under study. * Failure to comply with study procedures: Complete less than 70% of the days in the patient's diary and/or take less than 80% of the days of the study products. * Receive any of the unauthorized treatments indicated in the selection criteria, with the exception of antibiotics that will be allowed under medical prescription.