Smoking, vaping and hospitalization for COVID-19

Correspondence: papers@team.qeios.com — Qeios will forward to the authors

Introduction

There is a lot of speculation about the effects of smoking on Corona Virus Disease 2019 (COVID-19). Smoking increases susceptibility to respiratory infections and media reports suggest that it may increase the risk of being infected with acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19. SARS-CoV-2 is known to use the angiotensin converting enzyme 2 (ACE2) as a receptor for cell entry, and there is evidence that smoking downregulates ACE2 expression in the lung and other tissues.¹ China has a high prevalence of smoking (27.7%), much higher among males (52.1%) than females (2.7%).²

Methods

To examine how the prevalence of smoking among hospitalized COVID-19 compares to the smoking prevalence of the population, we searched the literature and identified 5 studies examining clinical features of hospitalized COVID-19 patients in China with data about the smoking status.^3-7 Prevalence of smoking among hospitalized patients was compared with the expected prevalence that was calculated based on the population smoking prevalence and gender of hospitalized cases using the formula: Expected smokers = (males x 0.521) + (females x 0.027).

Results

Findings are presented in Table 1. From a total 1546 hospitalized COVID-19 cases analyzed in the 5 studies included, 58.0% were males and 42.0% were females. The prevalence of current smoking was 10.2% (95%CI: 8.6-11.7%). However, the calculated expected prevalence of current smoking, considering the population prevalence in China was 31.3% (95%CI: 29.0-33.6%). The difference was statistically significant according to z-test (z-statistic: 17.89, P < 0.0001).

Discussion

The current study examined for the first time the prevalence of current smoking among hospitalized patients with COVI-19 in China and compared it with the expected prevalence based on the population smoking prevalence. Care was taken to consider the large difference between genders, with current smoking being substantially more prevalent among Chinese males than females. An unusually low prevalence of current smoking among hospitalized COVID-19 cases in China was observed when considering the population smoking prevalence. The true prevalence of current smoking among hospitalized COVID-19 cases presented in 5 studies was approximately one-third the expected prevalence. This preliminary analysis, assuming that the reported data are accurate, does not support the argument that current smoking is a risk factor for hospitalization for COVID-19, and might even suggest a protective role. The latter could be linked to the downregulation of ACE2 expression that has been previously known to be induced by smoking. However, other factors, such as socioeconomic status, should be considered in examining the access of smokers with COVID-19 to hospital care. Furthermore, disease progression, complications and death among hospitalized COVID-19 patients who are current smokers need to consider other comorbidities, such cardiovascular disease, which are risk factors for adverse COVID-19 outcomes and are more prevalent among current smokers. Currently available evidence does not allow for a multivariate analysis adjusted for such factors. It remains unclear whether smoking per se or other factors related to comorbidities may be responsible for an adverse outcome. No studies recording e-cigarette use status among hospitalized COVID-19 patients were identified. Thus, no recommendation can be made for e-cigarette users.

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