With some studies claiming that smokers might be protected against the new coronavirus, the World Health Organization (WHO) has issued a statement saying that smokers are more likely to develop severe disease with Covid-19 as compared to non-smokers. This is according to a review of studies by public health experts convened by WHO on April 29.
Tobacco smoking is a known risk factor for many respiratory infections and increases the severity of respiratory diseases. Stating that Covid-19 is an infectious disease that primarily attacks the lungs, WHO experts emphasize that smoking impairs lung function making it harder for the body to fight off coronaviruses and other diseases.
“Tobacco is also a major risk factor for noncommunicable diseases like cardiovascular disease, cancer, respiratory disease, and diabetes, which put people with these conditions at higher risk for developing severe illness when affected by Covid-19. Available research suggests that smokers are at higher risk of developing severe disease and death,” says the WHO.
A recent paper, which examined smoking rates among COVID-19 patients in a French hospital, hypothesized that smoking might make people less susceptible to the coronavirus. The researchers estimated the rates of daily current smokers in Covid-19-infected patients in a large French university hospital between February 28 and March 30 for outpatients, and from March 23 till April 9 for inpatients.
The inpatient group was composed of 343 patients, with a rate of daily smokers of 4.4%. The outpatient group was composed of 139 patients, and the daily smokers' rate was 5.3%. This was a fraction of the prevalence seen in the general French population, where the daily smokers' rate was 25.4%. “The rate of current daily smokers was significantly lower in Covid-19 outpatients and inpatients (80.3% and 75.4%, respectively), as compared to that in the French general population.
Our cross-sectional study in both Covid-19 out- and inpatients strongly suggests that daily smokers have a very much lower probability of developing symptomatic or severe SARS-CoV-2 (the virus that causes Covid-19) infection as compared to the general population,” the study concludes.
The finding of lower rates of smokers among Covid-19 cases has also been described in a rapid review of 28 studies on smoking in coronavirus patients from various countries. “Across 28 observational studies, there is substantial uncertainty arising from the recording of smoking status on whether current and/ or former smoking status is associated with SARS-CoV-2 infection, hospitalization, or mortality. There is low-quality evidence that current and former smoking compared with never is associated with greater disease severity in those hospitalized for Covid-19,” the authors say.
However, researchers at Baylor College of Medicine, the University of South Carolina and other institutions have identified tobacco smoking as a potential risk factor for infection of the Covid-19 virus. The research team analyzed datasets of the RNA expressed by various types of lung tissue, comparing the current and former smokers and non-smokers. They looked at the expression of ACE2, the molecule in the respiratory tract that the Covid-19 virus uses to attach to and infect human cells. They also looked at the expression of FURIN and TMPRSS2, human enzymes known to facilitate Covid-19 virus infection.
The researchers report a 25% increase in the expression of ACE2 in lung tissues from ever-smokers, people who have smoked at least 100 cigarettes during their lives when compared with nonsmokers. “Smoking also increased the presence of FURIN, but to a lower extent compared to ACE2. TMRPSS2 expression in the lungs was not associated with smoking.
Smoking remodeled the gene expression of cells in the lungs so that the ACE2 gene was more highly expressed in goblet cells, cells that secrete mucus in order to protect the mucous membranes in the lungs,” says the study published in the American Journal of Respiratory and Critical Care Medicine.
The significant “smoking effect on ACE2 pulmonary expression” identified in this study indicates not only an increase in the entry points for the Covid-19 virus but also may suggest an increased risk for viral binding and entry of the virus in the lungs of smokers, says the team.
Meanwhile, the WHO said that its experts are constantly evaluating new studies, including research that examines the link between tobacco use, nicotine use, and COVID-19. “WHO urges researchers, scientists, and the media to be cautious about amplifying unproven claims that tobacco or nicotine could reduce the risk of COVID-19. There is currently insufficient information to confirm any link between tobacco or nicotine in the prevention or treatment of COVID-19,” says the WHO.
It adds, “WHO stresses the importance of ethically approved, high-quality, systematic research that will contribute to advancing individual and public health, emphasizing that promotion of unproven interventions could have a negative effect on health.”
Commenting on the French study, Dr Maria Van Kerkhove, the WHO’s technical lead on Covid-19, reiterated during a briefing that smokers, if they do get infected with Covid-19, have a greater risk of severe disease and death.
“There are a number of studies out there that have been published that have found that smoking leads to the development of more severe disease, and puts people at higher risk of being put on a ventilator, being in ICU, and for dying. There are some media reports of two studies in particular that have not been peer-reviewed, that have looked at the prevalence of smoking in people who have been hospitalized and not. These studies did not evaluate, they were not designed to evaluate whether smoking was protective or not in any shape or form, and they do not say that smoking is protective,” says Dr Kerkhove.