• David Simons, Lion Shahab, Jamie Brown, and Olga Perski.
• Centre for Emerging, Endemic and Exotic Diseases, Royal Veterinary College, London, UK.
• Addiction. 2021 Jun 1; 116 (6): 1319-1368.

AimsTo estimate the association of smoking status with rates of (i) infection, (ii) hospitalization, (iii) disease severity and (iv) mortality from SARS-CoV-2/COVID-19 disease.DesignLiving 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.SettingCommunity or hospital, no restrictions on location.ParticipantsAdults who received a SARS-CoV-2 test or a COVID-19 diagnosis.MeasurementsOutcomes were SARS-CoV-2 infection, hospitalization, disease severity and mortality stratified by smoking status. Study quality was assessed (i.e. 'good', 'fair' and 'poor').FindingsVersion 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 [relative risk (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 hospitalization (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 hospitalization 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).ConclusionsCompared with never smokers, current smokers appear to be at reduced risk of SARS-CoV-2 infection, while former smokers appear to be at increased risk of hospitalization, increased disease severity and mortality from COVID-19. However, it is uncertain whether these associations are causal.© 2020 The Authors. Addiction published by John Wiley & Sons Ltd on behalf of Society for the Study of Addiction.

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