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 10)

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 10 (searches up to 15 December 2020) included 345 studies with 52 ‘good’ and ‘fair’ quality studies included in unadjusted meta-analyses. One-hundred-and-one studies (29.3%) reported current, former and never smoking status with the remainder using broader categories. 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 = 0.69, 95% Credible Interval (CrI) = 0.58-0.82, τ = 0.36). Data for former smokers were inconclusive (RR = 1.03, 95% CrI = 0.94-1.13, τ = 0.18) but favoured there being no important association (8% probability of RR ≥1.1). Former compared with never smokers were at increased risk of hospitalisation (RR = 1.18, CrI = 1.07-1.31, τ = 0.14), greater disease severity (RR = 1.52, CrI = 1.12-2.06, τ = 0.29) and mortality (RR = 1.40, 95% CrI = 1.20-1.64, τ = 0.19). Data for current smokers on hospitalisation, disease severity and mortality were inconclusive (RR = 1.08, CrI = 0.95-1.23, τ = 0.18; RR = 1.26, CrI = 0.85-1.93, τ = 0.34; RR = 1.05, 95% CrI = 0.77-1.41, τ = 0.39, respectively) but favoured there being no important associations with hospitalisation and mortality (31% and 38% probability of RR ≥1.1, respectively) and a small but important association with disease severity (80% probability of RR ≥1.1). Conclusions: Compared 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 hospitalisation, greater disease severity and mortality from COVID-19. However, it is uncertain whether these associations are causal