The association of smoking status with SARS-CoV-2 infection, hospitalisation and mortality from COVID-19: A living rapid evidence review with Bayesian meta-analyses (version 7)

<jats:p>Aims: To estimate the association of smoking status with rates of i) infection, ii) hospitalisation, iii) disease severity, and iv) mortality from SARS-CoV-2/COVID-19 disease.

Design: Living rapid review of observational and experimental studies with random-effects hierarchical Bayesian meta-analyses. Published articles and pre-prints were identified via MEDLINE and medRxiv.

Setting: Community or hospital. No restrictions on location.

Participants: Adults who received a SARS-CoV-2 test or a COVID-19 diagnosis.

Measurements: Outcomes were SARS-CoV-2 infection, hospitalisation, disease severity and mortality stratified by smoking status. Study quality was assessed (i.e. ‘good’, ‘fair’ and ‘poor’).

Findings: Version 7 (searches up to 25 August 2020) included 233 studies with 32 ‘good’ and ‘fair’ quality studies included in meta-analyses. Fifty-seven studies (24.5%) reported current, former and never smoking status. Recorded smoking prevalence among people with COVID-19 was generally lower than national prevalence. Current compared with never smokers were at reduced risk of SARS-CoV-2 infection (RR=0.74, 95% Credible Interval (CrI) = 0.58-0.93, τ = 0.41). Data for former smokers were inconclusive (RR=1.05, 95% CrI = 0.95-1.17, τ = 0.17) but favoured there being no important association (21% probability of RR ≥1.1). Former compared with never smokers were at somewhat increased risk of hospitalisation (RR=1.20, CrI = 1.03-1.44, τ = 0.17), greater disease severity (RR=1.52, CrI = 1.13-2.07, τ = 0.29), and mortality (RR=1.39, 95% CrI = 1.09-1.87, τ = 0.27). Data for current smokers were inconclusive (RR=1.06, CrI = 0.82-1.35, τ = 0.27; RR=1.25, CrI = 0.85-1.93, τ = 0.34; RR=1.22, 95% CrI = 0.78-1.94, τ = 0.49 respectively) but favoured there being no important associations with hospitalisation and mortality (35% and 70% probability of RR ≥1.1, respectively) and a small but important association with disease severity (79% probability of RR ≥1.1).

Conclusions: Due to incomplete recording of smoking status, there is uncertainty about the associations of smoking with COVID-19 outcomes. Current smokers were at reduced risk of SARS-CoV-2 infection. Former smokers were at increased risk of hospitalisation, disease severity and mortality from COVID-19, while data for current smokers inconclusively favoured no large associations with these outcomes.</jats:p>