Smoking and COVID-19 Scientific brief

This is an update to the Scientific Brief entitled ‘Smoking and COVID-19,’ originally published on 26 May 2020. Since its publication, a study entitled ‘Cardiovascular Disease, Drug Therapy, and Mortality in Covid-19’ by Mehra et al. has been retracted by the New England Journal of Medicine. This version of the Scientific Brief has removed the study from the review. The removal of this study from the review does not change the conclusions of the analysis.

Background The harms of tobacco use are well-established. Tobacco causes 8 million deaths every year from cardiovascularhttps://www.who.int/publications/i/item/WHO-2019-nCoV-Sci_Brief-Smoking-2020.2 diseases, lung 

disorders, cancers, diabetes, and hypertension.1 Smoking tobacco is also a known risk factor for severe disease and death from many 

respiratory infections.2-4 In the COVID-19 pandemic, questions have been asked about clinical outcomes for smokers, and whether 

they are equally susceptible to infection, and if nicotine has any biological effect on the SAR-CoV-2 virus (the virus that causes 

COVID-19).

5-7 At the time of writing, one clinical trial to test the effects of nicotine has been announced, but no trial registration 

record was found as of 12 May 2020. 

This review therefore assesses the available peer-reviewed literature on the association between smoking and COVID-19, including 

1) risk of infection by SARS-CoV-2; 2) hospitalization with COVID-19; and 3) severity of COVID-19 outcomes amongst 

hospitalized patients such as admission into intensive care units (ICU), use of ventilators and death.

Methods

A review was conducted on 12 May 2020 on smoking and COVID-19, using MEDLINE, EMBASE, Cochrane Library, and WHO 

Global Database. Quantitative primary research on adults or secondary analyses of such studies were included. Individual studies 

included in meta-analyses that were not otherwise identified in the search were sought.

Due to the preliminary nature of the many non-peer-reviewed reports issued during the COVID-19 pandemic, preprint repositories 

were deliberately excluded from this review.

Review of the evidence

Thirty-four peer-reviewed studies met the inclusion criteria. All included studies were in English. None examined tobacco use and 

the risk of infection or the risk of hospitalization. A total of 26 observational studies and eight meta-analyses were identified. All 

observational studies reported the prevalence of smoking amongst hospitalized COVID-19 patients. Two meta-analyses reported 

pooled prevalence of smoking in hospitalized patients using a subset of these studies (between 6 and 13 studies). 

Eighteen of the 26 observational studies containing data on smoking status by severity of COVID-19 outcomes. Six meta-analyses 

were identified that examined the association between smoking and severity of COVID-19. Nine of the 18 studies were included in 

the six meta-analyses of smoking and severity (five to seven studies in each analysis), resulting in 1,604 sets of patient data being 

reported more than once. All data in the six meta-analyses come from patients in China. 

What is the risk of smokers being infected by SARS-CoV-2?

There are currently no peer-reviewed studies that have evaluated the risk of SARS-CoV-2 infection among smokers. This research 

question requires well-designed population-based studies that control for age and relevant underlying risk factors. 

What is the risk of smokers being hospitalized for COVID-19? 

There are currently no peer-reviewed studies that directly estimate the risk of hospitalization with COVID-19 among smokers. 

However, 27 observational studies found that smokers constituted 1.4-18.5% of hospitalized adults.

8-32 Two meta-analyses have 

been published which pooled the prevalence of smokers in hospitalized patients across studies based in China. The meta-analysis 

by Emami et al.

33 analysed data for 2986 patients and found a pooled prevalence of smoking of 7.6% (3.8% -12.4%) while Farsalinos 

et al.

34 analysed data for 5960 hospitalized patients and found a pooled prevalence of 6.5% (1.4% - 12.6%).

For full article, visit the link below:

https://www.who.int/publications/i/item/WHO-2019-nCoV-Sci_Brief-Smoking-2020.2