Abstract

Background: In older patients, prevention of acute respiratory tract infections (RTIs) is challenging. Experimental studies have consistently underlined an immune-potentiating effect of the bacterial lysates product OM85, on both cellular and humoral responses.

Objective: This work aimed to assess the potential efficacy of OM-85 for RTIs’ prevention in older individuals.

Methods: This explorative longitudinal study included 24 patients aged 65 years or older recruited in the GeroCovid Observational Study- home and outpatient care cohort. For the study purposes, we included 8 patients treated with OM-85 from December 2020 to June 2021 (group A), and a control group of 16 patients, matched for sex and age, who did not receive bacterial lysates (group B). RTIs were recorded from the participants’ medical documentation in an e-registry from March 2020 to December 2021.

Results: In 2020, group A experienced a total of 8 RTIs, which affected 6 out of 8 patients (75%); group B reported 21 RTIs, with at least one event in 11 out of 16 patients (68.7%). In 2021, RTIs affected 2 out of 8 patients (25%) in group A (p < 0.02), and 13 out of 16 patients (81.2%) in group B (within this group, 5 patients had two RTIs). The RTIs' cumulative incidence over the observation period significantly differed between groups (66.7% in group A vs. 24.3% in group B; p < 0.002), as well as the decrease in RTIs frequency from 2020 to 2021. No patients in group A were affected by COVID-19 during the observation period, while among controls, two patients had SARS-CoV-2 infection, notwithstanding three doses of vaccine.

Conclusion: This study suggests that bacterial lysates may provide clinical benefits for preventing RTIs. Additional research involving larger cohorts is required to verify the effectiveness of OM-85 in preventing RTIs in older adults.

Keywords: OM-85, efficacy, older patients, respiratory tract infections, bacterial lysates, COVID-19.