Electronic cigarette use and risk of SARS-CoV-2 infection| Tabaccologia

Abstract

Introduction: Some researchers speculated that novel nicotine-containing products, such as electronic cigarettes and heated tobacco products, could lower the risk of SARS-CoV-2 infection. The aim of this study is to investigate the role of electronic cigarettes on SARS-CoV-2 infection.

Methods: We conducted a systematic literature review, updated to February 2023, using PubMed/ MEDLINE and Web of Science and a meta-analysis on all the studies providing data on the link between electronic cigarette and SARS-CoV-2 infection.

Results: Starting from 553 non-duplicate publications, we selected 13 original articles on the topic of interest. The pooled odds ratio (OR) of SARS-CoV-2 infection for electronic cigarette users vs. electronic cigarette never/non-users, based on 13 studies (4 cohort and 9 cross-sectional studies), was 1.31 (95% confidence interval, CI: 1.09-1.58).

Discussion: No evidence was found on the alleged protective role of electronic cigarette use on SARS-CoV-2 infection. On the contrary, electronic cigarette use is significantly associated with a 30% increased risk of infection.

Introduction

The World Health Organization (WHO), supported by several scientific studies, has highlighted the health risks associated with the use of electronic cigarettes (e-cig), particularly with regard to respiratory diseases [1-3]. In addition to uncertainties about their safety, there is considerable concern about the public health consequences of e-cig use, such as the renormalization of cigarette smoking and the use of these products among young people and former smokers, respectively, as a gateway to conventional cigarette smoking and as a trigger for relapse into addiction [1,4,5]. WHO also advises smokers against the use of e-cigs as a smoking cessation tool [1].

Studies conducted during the pandemic observed a relatively low prevalence of smokers among patients with COVID-19 [6]. Some researchers, whose link to the tobacco industry in some cases cannot be ruled out [7], hypothesized that nicotine might have a protective effect against SARS-CoV-2 infection, and consequently that e-cig use might reduce the risk of infection [8-10]. Moreover, a systematic review suggested the use of these nicotine-containing products to help smokers quit smoking as part of public health efforts during the COVID-19 pandemic [6]. To date, however, evidence on the role of e-cigs on SARS-CoV-2 infection is lacking.

This systematic review and meta-analysis were conducted to investigate the role of e-cig use on SARS-CoV-2 infection.

Methods

We conducted a systematic literature review on PubMed/MEDLINE and Web of Science (WoS), identifying all studies that provided data on the relationship between the use of novel nicotine-containing products (i.e., e-cigs and heated tobacco products) and the risk of SARS-CoV-2 infection or COVID-19 disease progression. For the purposes of this report, we only considered studies on the association between e-cig use and SARS-CoV-2 infection. In addition, we conducted a meta-analysis to quantify this association.

Publications written in a language other than English or not published in peer-review journals were excluded from the review. Studies that provided relative risks (RR), hazard ratios (HR), prevalence ratios (PR) or odds ratios (OR) of SARS-CoV-2 infection for e-cig users versus non-users were considered eligible for meta-analysis.

On 7 February 2023, using a search strategy designed for this study, we identified 437 publications in PubMed/MEDLINE and 442 publications in WoS. After removing duplicates, we obtained a total of 551 articles. After two screenings (the first from title and abstract, and the second from full-text), we identified 18 eligible articles, including two additional articles from other sources, that had not been identified by the literature search. Of these, 13 articles provided data on the risk of SARS-CoV-2 infection according to e-cig use, and were therefore considered eligible for the present meta-analysis.

We then used random-effects meta-analytical approaches to derive summary estimates of the OR of SARS-CoV-2 infection for e-cig users versus non-users. When necessary, we calculated OR estimates by grouping the ORs of different categories (e.g. dual and exclusive users, or regular and occasional users), using Hamling’s method [11]. We used I² statistics to assess heterogeneity between studies [12].

Results

The characteristics of the 13 studies presented in the included publications on the association between e-cig use and SARS-CoV-2 infection are shown in Table 1. The age range among the included studies was heterogeneous, with four publications focusing on adolescents or young adults. All but one study provided adjusted estimates of the measure of association.

The included studies provided information on a total of over 300,000 individuals and over 12,000 COVID-19 cases. The meta-analysis resulted in an aggregate OR of SARS-CoV-2 infection for e-cig users compared to non-users of 1.31 (95% confidence interval, CI: 1.09-1.58; Figure 1).

Discussion

This study shows the results of the first systematic review and meta-analysis to quantify the link between e-cig use and risk of SARS-CoV-2 infection, showing an absence of data supporting the presumed protective role of e-cig use on SARS-CoV-2 infection. In contrast, we found that e-cig users had a 31% higher risk of infection than non-users.

In a previous meta-analysis, Simons et al. found a reduced risk and an equivalent risk of testing positive for SARS-CoV-2 among current smokers and former smokers of conventional cigarettes compared to non-smokers, respectively [6]. In that systematic review, the authors, while also collecting data from studies on the association between e-cig use and risk of SARS-CoV-2 infection, did not provide an aggregated estimate of this association. However, they emphasised the role of novel nicotine-containing products to help smokers quit smoking as part of public health efforts during the COVID-19 pandemic. The results of our systematic review and meta-analysis show, in contrast to the recommendations provided by Simons et al., an increased risk of SARS-CoV-2 infection for e-cig users.

The main challenge and limitation of this systematic review concerns the high heterogeneity between the characteristics of the study population and between the definitions of e-cig use. With regard to population characteristics, some studies focused on students or young adults, whereas most were based on the adult population. As far as the definition of use is concerned, the use of e-cigs was reported in various forms (e.g., exclusive or dual use), so, when possible, we prioritised certain exposures or combined them to reduce heterogeneity. A further limitation of the meta-analysis is that most of the included studies were cross-sectional and only a few were prospective cohort studies, thus limiting the ability to provide evidence of a causal association between e-cig use and SARS-CoV-2 infection.

For future research on e-cigs and novel tobacco products, there is a need to establish standardised definitions of use, including dual-use or poly-use. The market for these products is growing rapidly and new ones are constantly emerging, about which little information is available. It is therefore important, when conducting scientific studies, to retrieve detailed information on the type of devices used.

A multicentre longitudinal study was conducted in 2020-2021 in 24 Italian hospitals on a total of 1,820 laboratory-confirmed COVID-19 patients to evaluate the association between e-cigarette, heated tobacco product (HTP) and second-hand smoke (SHS) exposure and COVID-19 progression (COvid19 and SMOking in Italy; COSMO-IT project) [26]. The study found an increased risk of COVID-19 mortality for smokers (compared with never smokers) and for SHS exposure (among non-smokers), and a non-significant increased risk of COVID-19 severity for e-cigarette users (OR 1.60; 95% CI, 0.96-2.67). These findings are consistent with the results of our systematic review.

In conclusion, our systematic review and meta-analysis is consistent with a 30% excess risk of SARS-CoV-2 infection for e-cig users compared to non-users, thus ruling out a possible protective role of the use of these devices. Given the widespread use of novel tobacco products, our results provide an additional reason to avoid, and advise against, their use.

Figures and tables

Figure 1.Forest plot of studies on the risk of SARS-CoV-2 infection for e-cigarette users compared to non-users. CI: confidence interval; OR: odds ratio.

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