Is there a smokers paradox in Covid-19?

 It is well established that cigarette smoking is associated with morbidity and mortality in several respiratory infections. However data from recent studies suggest that active smokers are underrepresented among patients with COVID-19. This has led to claims that a ‘smoker’s paradox’ may exist in COVID-19, wherein smokers are protected from infection and severe complications of COVID-19.

This review summarises existing literature in this context.

We identified several biases and knowledge gaps which may give the false impression that smoking is protective in COVID-19. As of now, the data supporting smoker’s paradox claims are limited and questionable.

Plausible biologic mechanisms by which smoking might be protective in COVID-19 include an anti-inflammatory effect of nicotine, a blunted immune response in smokers (reducing the risk of a cytokine storm in COVID-19) and increased nitric oxide in the respiratory tract (which may inhibit replication of SARS-CoV-2 and its entry into cells).

On the other hand, smoking may worsen susceptibility and prognosis in COVID-19, in a manner similar to other respiratory infections.

The claims of a protective effect must be viewed with extreme caution by both the general population as well as clinicians. Further investigations into the interaction between smoking and COVID-19 are warranted to accurately assess the risk of contracting COVID-19 among smokers, and progression to mechanical ventilation or death in patients suffering from it.

2021-01-06_06-16-20
bmjebm-2020-111492.full

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