The Effect of Smoking on COVID-19 Symptom Severity: Systematic Review and Meta-Analysis

Figure 2

(a) Prevalence of smoking in severe COVID-19 patients. (b) Funnel plot for meta-analysis of the prevalence of smoking in severe COVID-19 patients. (c) Prevalence of smoking among severe COVID-19 patients after the exclusion of studies by Qi et al. [16] and Zhang et al. [23]. (d) Funnel plot for the meta-analysis of smoking among severe COVID-19 patients after the exclusion of studies by Qi D et al. [16] and Zhang R et al. [23].

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