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

Figure 3

(a) Comparison of smoking status in severe COVID-19 patients. (b) Funnel plot for the meta-analysis of smoking among severe COVID-19 patients. (c) Comparison of smoking status among severe COVID-19 patients after the exclusion of a study by Zhang et al. [23]. (d) Funnel plot for the meta-analysis of smoking among severe COVID-19 patients after the exclusion of a study by Zhang et al. [23].

(a)

(b)

(c)

(d)