The study of 480 ill patients at the Pitié-Salpêtrière hospital in Paris - led by Professor of Internal Medicine Zahir Amoura - was published on Wednesday this week (April 22) on pre-publication site Qeios.
The study included 350 hospitalised patients, and 130 less-severe hospital outpatients, all of whom tested positive for Covid-19. The work looked at whether the patients smoked more or less than the average, wider population of the same sex and the same age.
Professor Amoura, who led the study, said that there were very few smokers among Covid-19 patients.
He said: “We had a level of smokers at about 5%, which is low. There are around 80% fewer smokers among patients of Covid-19 than the general population, of the same sex and same age.”
The results therefore suggest that there may be something in tobacco that acts as a protector against Covid-19.
Through a common contact - the Nobel-prizewinning physician Serge Haroche - Professor Amoura consulted globally-renowned neurobiologist and Académie des Sciences member Jean-Pierre Changeux, who suggested that nicotine could stop the virus from entering the cells of regular smokers.
Professor Changeux said: “The hypothesis is that nicotine appears to interfere with the coronavirus’ attachment to the nicotine receptor, which would therefore work against the spread of the virus.”
William Lowenstein, lung specialist and president of addiction prevention group SOS Addiction, said: "This competition between nicotine and the virus, on this receptor, could explain the spectacular under-representation of smokers among people infected with the coronavirus."
This theory is now set to be tested via a wider clinical trial, with tests beginning imminently. Nicotine patches are to be given to three different groups; to health workers, as a preventative measure; to hospitalised patients; and to those in intensive care.
Nicotine may also diminish the excessive immune response to the virus seen in some patients, which can cause fatal consequences, it is suggested.
However, the public is warned that despite any possible preventative effects of nicotine, smoking remains otherwise very damaging to health.
The data should still be considered with caution, as more studies need to be done to establish a real link between Covid-19 and nicotine.
Marion Adler, a tobaccologist at the Antoine-Béclère hospital in Clamart (Hauts-de-Seine), said: "We have to be very cautious, because at the moment we only have a few pieces of scientific data."
She added: "It appears to be nicotine that protects, not smoking. Tobacco is still toxic."
Mr Lowenstein of SOS Addiction said: "There is no question that people should smoke to protect themselves from the virus."
Even in the original study, Professors Amoura and Changeux said: "Smoking causes severe problems and remains dangerous to health."
Smoking is still one of the major causes of avoidable deaths in France, with figures from health authority Santé Publique France showing it is linked to 75,000 deaths per year.
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