Coronavirus: why you have to be careful with the study which suggests that nicotine can slow down Covid-19

A study of some 480 Covid-19 patients shows that smokers are less affected by the virus.  Studies on the effects of nicotine should be carried out.

Does Nicotine Protect Against Coronavirus?  This is the hypothesis considered by the neurobiologist Jean-Pierre Changeux, member of the Academy of Sciences, and Zahir Amoura, specialist in internal medicine, in a study available in prepublication on the Qeios platform (in English), Tuesday April 21  .

This hypothesis emerged after the discovery of the low proportion of smokers among patients with Covid-19.  A study carried out by a team from the Pitié-Salpêtrière hospital in Paris among 482 Covid-19 patients revealed that only 5% of them were daily smokers.  From there to deduce a virtuous role of nicotine against the coronavirus?  It is not that obvious.  Franceinfo explains to you why this data should be taken with caution.

Because the data is incomplete

Studies in China have already suggested that smokers are less infected with the coronavirus.  A first study mentioning it, published on February 24 in The Lancet, involved 709 patients in Wuhan.  Another, published in the New England Journal of Medicine on February 28, profiles 1,099 patients.  In both cases, the share of smokers is lower than in the general population.

In these studies, patient smoking data were not cross-referenced with age and sex, which may distort cause and effect relationships.  French researchers have therefore attempted to clarify the correlation between tobacco consumption and the probability of contracting the coronavirus.  Their study is available in prepublication on the Qeios platform.

They calculated the rate of smokers in 139 patients tested positive for Covid-19, placed on an outpatient basis with mild symptoms, and in 343 other more serious patients, hospitalized in Pitié-Salpêtrière (excluding intensive care services).  The scientists then observed whether these patients were more or less numerous than the smokers in the general population of the same sex or the same age.

4.4% of hospitalized patients with a median age of 65 are daily smokers.  They are 5.3% among ambulatory patients, whose median age is 44 years.  "Basically, we have 80% fewer smokers in Covid patients than in the general population of the same sex and the same age," says Zahir Amoura, from France Inter.  "Our cross-sectional study strongly suggests that daily smokers have a much lower probability of developing a symptomatic or serious infection with Sars-CoV-2 compared to the general population," write the authors.

However, the low number of daily smokers among the patients observed does not allow us to conclude that there is a correlation between daily tobacco consumption and the severity of the coronavirus infection.  The authors also recognize that their work does not take into account patients in intensive care, and that a larger study is necessary.