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 8)

<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 8 (searches up to 22 September 2020) included 256 studies with 36 ‘good’ and ‘fair’ quality studies included in meta-analyses. Sixty-seven studies (26.2%) 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=0.72, 95% Credible Interval (CrI) = 0.57-0.89, τ = 0.40). Data for former smokers were inconclusive (RR=1.02, 95% CrI = 0.92-1.13, τ = 0.18) but favoured there being no important association (7% probability of RR ≥1.1). Former compared with never smokers were at somewhat increased risk of hospitalisation (RR=1.19, CrI = 1.03-1.43, τ = 0.17), greater disease severity (RR=1.52, CrI = 1.12-2.05, τ = 0.29) and mortality (RR=1.35, 95% CrI = 1.09-1.73, τ = 0.26). Data for current smokers on hospitalisation, disease severity and mortality were inconclusive (RR=1.06, CrI = 0.82-1.35, τ = 0.27; RR=1.26, CrI = 0.85-1.96, τ = 0.34; RR=1.10, 95% CrI = 0.69-1.67, τ = 0.50, respectively) but favoured there being no important associations with hospitalisation and mortality (35% and 51% probability of RR ≥1.1, respectively) and a small but important association with disease severity (79% 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.</jats:p>