This study aims to evaluate the effectiveness of PMBL in reducing the occurrence of Respiratory Tract Infections, which are illnesses that affect the nose, throat, or lungs. The investigation involves comparing the use of Ismigen, a medication containing several bacteria such as Haemophilus influenzae, Klebsiella pneumoniae, Neisseria catarrhalis, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus viridans, and Klebsiella ozaenae, against a placebo. These medications will be administered as sublingual tablets, which are tablets that are placed under the tongue to dissolve.

During the course of the study, participants will be divided into groups to receive either the test medication or the placebo. The observation period includes a treatment phase during the fall and winter months, followed by a period to monitor health after the treatment has ended. The focus is on observing how often these infections occur and the duration of any illnesses experienced during this time.