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Risk of COVID-19 and smoking
  1. Ivan Berlin1,2
  1. 1 Department of Pharmacology, Hôpital Pitié-Salpêtrière-Sorbonne Université, Paris, France
  2. 2 Centre Universitaire de Médecine Générale et Santé Publique, UNISANTE, Université de Lausanne Faculté de Biologie et Médecine, Lausanne, Switzerland
  1. Correspondence to Dr Ivan Berlin, Department of pharmacology, Hôpital Pitié-Salpêtrière-Sorbonne Université, Paris 75013, France;{at}

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To the Editor

According to several reports, peer-reviewed or in preprint servers, smokers are under-represented among individuals tested positive (reverse transcription (RT)-PCR) for SARS-CoV-2 and diagnosed with COVID-19. Hippisley-Cox et al 1 also report a markedly reduced prevalence of light, moderate and heavy smokers among those tested positive for SARS-CoV-2 or admitted to an intensive care unit, findings similar to those reported by de Lusignan et al.2 The association does not seem to be dose-dependent/exposure-dependent,1 unlike the usually dose-dependent/exposure-dependent smoking–health disorder associations. These findings led to the hypothesis that, counterintuitively, smoking may have a protective effect against catching the infection. This supposedly protective effect should be ascertained before speculating about potential biological mechanisms.

This under-representation may come from several biases.3 4 One of them is the likelihood of more frequent testing among smokers due to their symptoms that are suggestive of COVID-19.2 A recent report shows that this is the case. Among young smokers, electronic cigarette (EC) users or dual users (tobacco+EC), the odds of testing for SARS-CoV-2 ranges from 3.25-fold to 9.16-fold compared with never smokers/users.5

Because the association of COVID-19 testing or COVID-19 with smoking status was not the aim of any of these1 2 or the previous reports, the assessment of smoking-related characteristics might lack accuracy3 4: recording secondary characteristics in an emergency situation is difficult, smokers who stopped very recently could be classified as former smokers, prevalence is based on self-report without biochemical verification of smoking status, and so on. Moreover, none of the reports included a control group of patients without COVID-19 and with the same demographic and comorbidity characteristics.

One can also wonder about the specificity of these findings because the number of individuals with alcohol use disorder is also lower among those with positive RT-PCR results.6

The protective effect of current smoking or current nicotine use (nicotine replacement therapy, EC use with nicotine) can only be ascertained by prospective studies.



  • Contributors IB is the sole author of this letter.

  • Funding The author has not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Patient consent for publication Not required.

  • Provenance and peer review Commissioned; internally peer reviewed.

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