Smoking links to the severity of COVID-19: An update of a meta-analysis.

Dear Editor,

The paper entitled “The impact of COPD and smoking history on the severity of COVID‐19: A systemic review and meta‐analysis.” published in Journal of Medical Virology on 15 April 2020. The results revealed the pooled odds ratio (OR) of chronic obstructive pulmonary disease and the development of severe coronavirus disease 2019 (COVID‐19) was 4.38 (fixed‐effect model, 95% confidence interval [CI]: 2.34‐8.20), while the OR of ongoing smoking was 1.98 (fixed‐effect model, 95% CI: 1.29‐3.05). However, in the sensitivity analysis, by excluding each study one by one showed that the study from Guan et al was a major source of heterogeneity. After excluding this study, the effect of smoking on the severity of COVID‐19 became insignificant with the OR of 1.55 (95% CI: 0.83‐ 2.87). The authors identified seven studies , , , , , , with data on smoking history and severity of COVID‐19. The searching for English and Chinese database was up to 22 March 2020.

In this letter, the author used the keywords “smoking,” “tobacco,” “smoker,” “COVID‐19,” “novel coronavirus,” and “SARS CoV‐2” to search PubMed on 16 April 2020. One new study published by Wang et al was identified. The updated meta‐analysis was performed by RevMan Ver. 5.3. The pooled OR of the fixed‐effect model was 2.16 (95% CI: 1.45‐3.22). The heterogeneity was smaller than that of the original analysis (I 2: 39% vs 44%). The sensitivity analysis excluding the study from Guan et al revealed a pooled OR of 1.89 (95% CI: 1.10‐3.24) (Figure 1). The heterogeneity increased in the sensitivity analysis (I 2 = 48%). The new study from Wang et al contributed a positive effect to the meta‐analysis (OR: 3.93, 95% CI: 1.30‐11.93) and resulted in the statistical significance. The study from Guan et al contributed to most of the cases in the meta‐analysis (1085 out of 1851 cases). By excluding this study, the results were more robust.

Figure 1

Forest plot of the sensitivity analysis of the updated meta‐analysis. 95% CI, confidence interval

The possible mechanisms linking smoke to the outcome of COVID‐19 were under study. A recent review suggested smokers are vulnerable to respiratory infection because of impaired immunity. Smoking can upregulate angiotensin‐converting enzyme‐2 receptor, the known receptor for the severe acute respiratory syndrome (SARS)‐coronavirus, and also possible for SARS‐CoV‐2 causing COVID‐19.

The results of the updated meta‐analysis further confirmed the impact of smoking history on the severity of COVID‐19.

CONFLICTS OF INTEREST

The author declares that there is no conflicts of interest.