Abstract
INTRODUCTION: Influenza is a major global health concern, responsible for up to 650 000 respiratory-related deaths annually. Although influenza is often perceived as mild in healthy adults, it can cause severe outcomes in high-risk groups, such as older adults, young children, pregnant women and those with underlying medical conditions. Various clinical, sociodemographic and environmental factors influence the progression to severe outcomes, whereas resilience factors, such as vaccination, may reduce risks. Despite growing research, the evidence base regarding risk and resilience is spread across many different aspects of the literature. This umbrella review will synthesise evidence from existing systematic reviews and meta-analyses to identify key risk and resilience factors associated with the progression of influenza to severe outcomes in the general population. METHODS AND ANALYSIS: This umbrella review follows the Joanna Briggs Institute (JBI) and Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols guidelines. We will include systematic reviews and meta-analyses reporting host-related risk or resilience factors for severe influenza outcomes. Four databases (EMBASE, Scopus, Medline and CINAHL) will be searched for English-language publications. Study quality will be assessed using AMSTAR 2, and the body of evidence will be evaluated using Grading of Recommendations Assessment, Development and Evaluation. Due to heterogeneity, findings will be analysed narratively. Risk and resilience factors will be grouped into demographic, clinical, behavioural, social and psychological domains. ETHICS AND DISSEMINATIONS: No ethical approval is required. The completed review will be shared through peer-reviewed journals and conference presentations. PROSPERO REGISTRATION NUMBER: CRD420250644475.