What Is the Risk of Developing a Severe Form of COVID-19 Infection Among Adults Who Currently Smoke Compared to Ex-smokers? Protocol for a Systematic Review and Meta-analysis

Abstract

Introduction: Smoking is associated with an increased risk of chronic diseases and poorer outcomes in patients with COVID-19. Although lung function improves after smoking cessation, evidence directly comparing COVID-19 severity between current and former smokers remains limited.

Objective: This systematic review aims to synthesize available evidence on the risk of developing severe COVID-19 among current smokers compared with former smokers.

Methods and Analysis: This review will follow the PRISMA-P 2015 guidelines. Non-randomized studies published from December 2019 onward will be systematically searched in PubMed, Cochrane CENTRAL, Embase, and Epistemonikos. Additional studies will be identified through grey literature sources, relevant journals, and reference list screening. Eligible studies must report outcomes for both current and former smokers and include at least one marker of severe COVID-19: ICU admission, assisted ventilation, or death. Two reviewers will independently screen studies and extract data. Risk of bias will be assessed using the Newcastle–Ottawa Scale, and the GRADE framework will be applied to evaluate the certainty of the evidence. Statistical analyses will be conducted using R version 4.3.2. Heterogeneity will be quantified using the I² statistic; a fixed-effect model will be used when heterogeneity is low, and a random-effects model will be applied otherwise. As this review will use published data, ethical approval is not required. PROSPERO Registration Number: CRD42022368552.