The growing epidemic of the respiratory virus covid-19 has been accompanied by public health messages focusing on how to best reduce the spread of the causative agent, SARS-CoV-2. So far, public health efforts have tended to emphasise key health behaviours such as covering one’s mouth when coughing, hand washing, social distancing, and reduced hand-to-hand contact. However, the role of tobacco smoking in the spread and exacerbation of covid-19 has received little attention to date.
Covid-19 is predominantly a disease of the respiratory tract, with emerging evidence indicating that cellular entry, viral replication and virion shedding occurs within the respiratory tract.  The virus has been shown to enter cells using the ACE-2 receptor, which is abundant in mucosal epithelial cells and the lung alveolar tissue.  Research on a similar respiratory virus, respiratory syncytial virus, has shown that inhaled tobacco smoke increases the rate of transmission and severity of viral respiratory tract infections.  Hence, it has been argued that smokers are at increased risk of contracting covid-19. Notably, smoking involves repetitive hand-to-face movements, which provide a route of entry for viral capsules. Smoking rates in countries that report sizable outbreaks of covid-19 (e.g. China, South Korea, Italy) remain high at approximately 19-27% of the population. 
Definitive evidence on whether current smokers are at increased risk of disease, morbidity and mortality from covid-19 are, to our best knowledge, not yet available. An article reporting disease outcomes in 1,099 laboratory confirmed cases of covid-19 reported that 12.4% (17/137) of current smokers died, required intensive care unit admission or mechanical ventilation compared with 4.7% (44/927) among never smokers.  Smoking prevalence among men in China is approximately 48% but only 3% in women; this is coupled with findings from the WHO-China Joint Mission on Coronavirus Disease 2019, which reports a higher case fatality rate among males compared with females (4.7% vs. 2.8%). [6,7] It is plausible that rates are even higher in subgroups of the population in which high mortality from SARS-CoV-2 infection is observed (e.g. those with extant cardiovascular and respiratory conditions such as chronic obstructive pulmonary disease). This needs to be further examined.
In the meantime, we strongly recommend that public health messages focused on how to curb the spread of SARS-CoV-2 also include country specific, evidence-based smoking cessation advice (e.g. https://quitnow.smokefree.nhs.uk/). Smoking has many negative effects on heart function and circulation and there is high quality evidence that preoperative smoking cessation interventions can lead to significant health benefits.  Smoking cessation at any time represents a huge opportunity for public health, with smokers tending to lose at least ten years of life.  It is likely that the current concern about the covid-19 epidemic provides a “teachable moment” in which smokers may be uniquely receptive to stop smoking advice. Smoking cessation mass media campaigns are ordinarily cost-effective, but budgets in England have been heavily reduced in recent years.
In addition to the health benefits of stopping smoking, it is plausible that a spike in quit rates could help reduce community transmission of SARS-CoV-2. During viral epidemics, evidence suggests that multipronged approaches involving both pharmacological and behavioural interventions (e.g. travel restrictions, school closures, vaccination) are best able to bring the reproductive number below 1.  We hence believe that high quality smoking cessation advice should form part of public health efforts during epidemics of respiratory viruses such as covid-19.
David Simons is a medical doctor with an interest in the human drivers of infectious disease emergence. He has an MSc in Tropical Medicine and International Health from the London School of Hygiene and Tropical Medicine and is currently pursuing a PhD in the epidemiology of emerging zoonotic diseases at the Royal Veterinary College. Twitter: @David_Simons_UK
Olga Perski is a Research Associate in the UCL Tobacco and Alcohol Research Group (UTARG). She specialises in the development and evaluation of digital tools to help people quit smoking and reduce their alcohol consumption. Twitter: @OlgaPerski
Jamie Brown is Professor of Behavioural Science and Health and Co-Director of the UCL Tobacco and Alcohol Research Group (UTARG). UTARG studies population-level trends and policies relating to smoking cessation and develop novel digital support tools. Twitter: @jamiebrown10
Role of funding source
DS is supported by a grant from the Biotechnology and Biological Sciences Research Council [BB/M009513/1].
Conflicts of interest
DS and OP have no conflicts of interest to declare. JB has received unrestricted research funding from Pfizer to study smoking cessation.
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