Protocol for a systematic review and meta-analysis of long influenza following the last five influenza pandemics.

INTRODUCTION

Influenza pandemics have been evaluated in terms of acute disease, while giving limited attention to long-term consequences. Renewed interest in postviral conditions following the COVID-19 pandemic highlights the need to reassess earlier influenza pandemics from a long-term perspective. This protocol describes a forthcoming systematic review and meta-analysis examining long-term health outcomes following exposure to five influenza pandemics. The aim is to assess the magnitude, consistency, mechanisms and determinants of postpandemic health outcomes.

METHODS AND ANALYSIS: This protocol followed the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) 2015 checklist. The planned systematic review and meta-analysis resulting from the protocol will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 checklist. Nine databases were searched using the PEO (Population, Exposure and Outcome) framework. Eligible studies include peer-reviewed quantitative observational and clinical follow-up studies reporting long-term outcomes. Two investigators will independently screen and select studies, extract data and assess quality. Study quality and risk of bias will be evaluated using the Newcastle-Ottawa Scale (NOS) and publication bias will be assessed using Egger’s and Begg’s tests. Narrative synthesis will be conducted before quantitative pooling. Fixed- and random-effects meta-analysis, meta-regression and Bayesian models will be applied to examine heterogeneity across populations, pandemics and outcomes.

ETHICS AND DISSEMINATION: This systematic review and meta-analysis do not require ethical approval, as it uses data from previously published studies (Head of department e-mail: elno@oslomet.no). The results will be published as a peer-reviewed article.

SYSTEMATIC REVIEW REGISTRATION: This systematic review protocol was registered in PROSPERO under registration number CRD420251267816.