Possible Viral Interference Leading to Protection from Subsequent Respiratory Viral Infections – Results of an Observational Study at a Singapore Teaching Hospital

Introduction: Respiratory infections, affecting mainly young children and the elderly, pose significant global health threats. While protection from related strains of viruses like influenza is well-documented, cross-protection among different viruses remains less understood. The disappearance of influenza during the COVID-19 pandemic prompted investigation into viral interference and non-pharmaceutical interventions' role. Studies suggest interactions between different viruses and host responses influence infection rates. In a large retrospective review, we assessed the impact of initial respiratory infections on subsequent viral infections, studying prevalent viruses including Influenza, Adenovirus, EV/RV, Parainfluenza, RSV, and coronaviruses. This aimed to elucidate the dynamics of viral interference independent of pandemic-related interventions. Methods: We analysed all patients tested for positive respiratory viruses between January 2016– December 2019 just prior to the pandemic in the National University Hospital laboratory, Singapore. Nasal, throat, and/ or nasopharyngeal swabs were collected by treating clinicians and tested by either multiplex PCR or immunofluorescence. Survival plots were created to study the time for a second viral infection following the initial respiratory viral detection. Results: RSV (HR: 0.63, 95%CI: 0.43–0.92; p