What is Happening with Smokers and COVID-19? A Systematic Review and a Meta-Analysis

Abstract

SARS-CoV-2 is a new coronavirus that has caused a worldwide pandemic. It produces severe acute respiratory disease (COVID-19), which is fatal in many cases, characterised by cytokine release syndrome (CRS). According to the World Health Organization (WHO), those who smoke are likely to be more vulnerable to infection. Here, in order to clarify the epidemiologic relationship between smoking and COVID-19, we present a systematic literature review until 28 April 2020 and a meta-analysis. It includes 18 recent COVID-19 clinical and epidemiological studies based on smoking patient status from 720 initial studies in China, USA, and Italy. The percentage of hospitalised current smokers was 7.7% (95%CI: 6.9-8.4) in China, 2.3% (95%CI: 1.7-2.9) in the USA and 7.6% (95%CI: 4.2-11.0) in Italy. These percentages were compared to the smoking prevalence of each country and statistically significant differences were found in them all (p <0.0001). By means of the meta-analysis, we offer epidemiological evidence showing that smokers were statistically less likely to be hospitalised (OR=0.18, 95%CI: 0.14-0.23, p<0.01). CRS and exacerbated inflammatory response are associated with aggravation of hospitalise patients. In this scenario, we hypothesise that nicotine, not smoking, could ameliorate the cytokine storm and severe related inflammatory response through the cholinergic-mediated anti-inflammatory pathway.

Comparison of Clinical, Laboratory and Radiological Findings in Iranian Smokers and non- Smokers Patients with COVID-19: A Case Control Study

“…A systematic review conducted by Rubio et al demonstrated that the proportion of smokers among COVID-19 patients is signi cantly lower than the percentage of smokers among general population in three different countries including China, Italy and the USA. Thus, they postulated that smokers are signi cantly less likely to develop severe disease and be hospitalized (16). The proposed mechanism is that nicotine can alleviate the ongoing in ammatory responses and cytokine storm in COVID-19 patients through the cholinergic anti-in ammatory pathway.…”

“…Many studies suggest that smoking makes individuals more susceptible to COVID-19 and results in higher risk of severe disease and ICU admission (11,(13)(14)(15). Whereas, some studies implicate that not only smoking does not cause harm but also can have a protective role for patients with COVID-19, due to anti-in ammatory effects of nicotine (6,16,17). Therefore, the exact in uence of smoking on patients with COVID-19 still remains unknown.…”

A Systematic Review and Meta-Analysis of Hospitalised Current Smokers and COVID-19

“…The authors thank Isabel Najera, Jose Antonio Najera, and Julio Basulto for helpful comments that greatly improved the manuscript. This manuscript was released as Pre-print at https://www.preprints.org/ manuscript/202004.0540/v1 on 2020/04/30 that has not been peer-reviewed [92].…”

Why Do Some Reports Claim that the Number of COVID-19 Hospitalized Smokers is Smaller than Expected?

“…However, a systematic review and meta-analysis published recently claims that the findings of 18 recent COVID-19 clinical and epidemiological studies show that smokers were statistically less likely to be hospitalized (OR=0.18, 95%CI: 0.14-0.23, p<0.01) [ 7 ]. Thus, the authors state: “The number of hospitalized smokers was smaller than expected based on the smoking prevalence in the different countries.…”