Influenza virus is a member of the orthomyxovirus family and causes an acute viral disease of the respiratory tract. The illness is usually self-limiting. Hospitalization and deaths mainly occur in high-risk groups (elderly, chronically ill). Response to vaccination is subject to high levels of variability due to age, stress, nutritional stage, etc.~Lactic acid bacteria are naturally commensal bacteria in the small and large intestines. These bacteria protect the host against potential pathogens by competitive exclusion and also by the production of antibacterial agents known as bacteriocins. It has only been recently shown that another mechanism whereby probiotic bacteria may provide a health benefit is by modulating immune responses.~Lactobacillus casei strain Shirota (LcS) is widely consumed in fermented milk products. Several studies, in animals as wells as in humans, report on the immunomodulatory functions of LcS.~The aim of this multicentre, randomized, placebo controlled, double blind study (RCT) is to assess if probiotic treatment with Lactobacillus casei Shirota improves the protection against influenza(-like) infections after vaccination with trivalent influenza vaccine in elderly residing in nursing homes.~Trial endpoints:~Clinical outcome: difference in incidence in upper respiratory tract infections (influenza-like illness)~Serological outcome: difference in influenza vaccine specific serum IgG between probiotic and control treatment
The purpose of this study is to determine whether probiotic treatment improves the protection against respiratory infections after influenza vaccination in elderly living in nursing homes.