A literature search was conducted using the PubMed databases to collect placebo-controlled randomized clinical trials related to recurrent respiratory tract infections in susceptible children with a deadline of March 1, 2021. The search keywords included pidotimod, OM-85 BV and bacterial lysate. The endpoint for this study were the frequency or number of respiratory tract infections..

A total of 14 studies with 28 treatment arms and 2400 subjects were included in the analysis. Among these studies, 5 reported pidotimod-related results and 9 reported OM-85 BV-related results.