Smoking and the risk of COVID-19 in a large observational population study

Abstract

BACKGROUND Smokers are generally more susceptible to infectious respiratory diseases and are at higher risk of developing severe complications from these infections. Conflicting reports exist regarding the impact of smoking on the risk of Coronavirus disease 2019 (COVID-19) infection. METHODS We carried out a population-based study among over 3,000,000 adult members of Clalit Health Services, the largest health provider in Israel. Since the beginning of the disease outbreak, 114,545 individuals underwent RT-PCR testing for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), and 4.0% had positive results. We performed a case-control study among patients who underwent SARS-CoV-2 testing, to assess the impact of smoking on infection incidence and severity. Individuals with positive tests were matched in a 1:5 ratio to individuals tested negative, of the same sex, age, and ethnicity/religion. Conditional logistic regressions were performed to evaluate odds ratios for current and previous smoking on the risk of testing positive. Multivariable logistic regressions were performed among patients infected with COVID-19 to estimate the association between smoking and fatal or severe disease requiring ventilation. Regressions were performed with and without adjustment for preexisting medical conditions. RESULTS In the matched cohort, current smokers (9.8%) were significantly less prevalent among members tested positive compared to the general population, and to matched members tested negative (19.4%, P<0.001). Current smoking was associated with significantly reduced odds ratio (OR) for testing positive OR=0.457 (95% confidence interval (CI) 0.407-0.514). Among patients tested positive, there was no evidence of significantly increased risk of developing severe or fatal disease. CONCLUSION The risk of infection by COVID-19 appears to be reduced by half among current smokers. This intriguing finding may reveal unique infection mechanisms present for COVID-19 which may be targeted to combat the disease and reduce its infection rate.

Systematic review of the prevalence of current smoking among hospitalized COVID-19 patients in China: could nicotine be a therapeutic option? Reply

“…In fact, we emphasized that no conclusion can be drawn about the prevalence of current smoking among patients with less severe COVID-19 that would not require hospitalization. While we suggested that nicotine is unlikely to have direct antiviral activity and, thus, is not expected to act as chemoprophylaxis, recent studies suggest that smokers may be less likely to be diagnosed with COVID-19 [3], while an inverse association between national smoking rates and COVID-19 mortality was reported [4]. These findings may not be in agreement with the report by Dr. Takagi but, in any case, the overall incidence of COVID-19 (including mild forms of the disease) should be clearly differentiated from severe COVID-19 that requires hospitalization.…”

Understanding Spatial Variation in COVID-19 across the United States

“…The left-side panels of Figure 2 confirm these findings and extend them over time by plotting the average residuals from regressions of log(1+cases) and log(1+deaths) on log population, since March 15, for jurisdictions with different political orientations. 13 We see a large political divide for both cases and deaths, which persists over time and even increases when it comes to deaths. Obviously, these patterns do not represent a causal effect of political orientation on disease severity.…”

“…See for instance Bursztyn et al (2020) and Allcott et al (2020). 13 Red counties are defined as those with a 2016 Trump vote share greater than 55%, blue counties are those with a Trump vote share smaller than 45%, and purple counties represent the balance. 14 Table A12 carries out similar regressions using the set of counties 70 days from onset (for cases -Panel A) and 60 days from onset (for deaths -Panel B).…”

COVID-19 and Obesity: Dangerous Liaisons

“…html). Advanced age, male sex, and the presence of multiple comorbidities have been clearly identified as major risk factors for the development of severe COVID-19 [3][4][5], whereas counter-intuitive evidence shows reduced COVID-19 hospitalizations among smokers [6][7][8].…”