It is common knowledge by now that smoking is not just injurious to health but also worsens outcomes in Covid patients. Evidence started emerging as early as June 2020, when a review for the World Health Organization (WHO) said smoking is associated with severe illness and an increased risk of death in hospitalized persons.
However, there were a number of papers and pre-prints (non-peer reviewed studies), starting from the early days of the pandemic, that attempted to understand the role of smoking in the disease progression. Some early studies concluded that smoking conferred some form of protection against Covid, whether it be against catching it or dying of it.
One such study was published in the European Respiratory Journal in July 2020.
The study stated that smokers were less likely to contract Covid-19 and, significantly, were not associated with the adverse outcomes of ICU admission, ventilation, or death. It joined a series of studies that are generating a worldwide flurry of interest, but last month the journal published a retraction. It took this action because two of the article’s five authors had not disclosed they had financial ties with the tobacco industry.
The study and the retraction
The study was retrospective — that is, it looked at already existing data to try and draw patterns from it. It was first published in the journal as a pre-print and then as an “early view”. What it did was to analyse data from 2,36,439 patients in Mexico who were suspected to have viral respiratory disease in February of 2020. As many as 89,756 (38 per cent) of them got diagnosed with Covid-19. After understanding the underlying conditions, the authors concluded that the Covid-19 patients were “disproportionately older, males and with increased prevalence of one or more co-morbidities, particularly diabetes, obesity, and hypertension”.
Additionally, the study reported that current smokers were 23 per cent less likely to get diagnosed with Covid, compared to non-smokers. It also said smokers were not associated with the adverse outcomes of ICU admission, ventilation, or even death.
Last month, the Journal announced that two of the study’s five authors had not disclosed potential conflicts of interest in the form of financial ties to the tobacco industry.
The vaping connection
The retraction notice reads: “One of the authors at the time had a current and ongoing role in providing consultancy to the tobacco industry on tobacco harm reduction; and another at the time was a principal investigator for the Greek NGO, NOSMOKE, which has its base at Patras Science Park, a science and innovation hub that has received funding from the Foundation for a Smoke Free World (an organization funded by the tobacco industry).”
Retraction Watch reports that the authors intend to submit the paper to another journal.
The senior author of the article, Greek public health specialist Konstantinos Farsalinos, according to Retraction Watch, a database supported by the Center for Scientific Integrity, was “a fairly prominent name in the world of vaping research”. Proponents of vaping have been touting the protective effect of nicotine against Covid-19.
Another study was retracted within a couple of months of the pre-print coming out last year. It suggested that smokers are protected from symptomatic disease. No other studies examining the effects of smoking on Covid patients have been listed on Retraction Watch.
Other similar studies
Farsalinos, one of the five authors of the journal who was connected with vaping research, had co-authored a similar paper based on Chinese data earlier. This paper analyzed patients hospitalized in China and concluded that “unexpectedly low prevalence of current smoking was observed among patients with COVID-19 in China, which was approximately 1/4th the population smoking prevalence.
The study added to headlines about the benefits of smoking in the face of Covid-19, but it was not the first one to do so.
One of the earliest pre-prints to come out in April 2020 was a retrospective study that analyzed patients hospitalized in France in February and March. It concluded that “daily smokers have a very much lower probability of developing symptomatic or severe SARS-CoV-2 infection”.
Some of these articles, which were even peer reviewed, attempted to investigate why smokers seemed to be protected. Nicotine, they speculated, most likely blocks the ACE2 receptor the virus’s spike protein uses to enter human cells.
These stories set off a maelstrom of media interest and were reported widely all over the world, with the stories concluding that smokers are at a lower risk of becoming seriously ill.
Such studies come with limitations
The problem with such studies is that they are riddled with confounders, or parameters that are not apparent upon a superficial examination of data.
Most of these studies tend to be retrospective analyses rather than randomized controlled trials. This leads to non-similar comparisons, which could often miss out on factors such as socio-economic backgrounds, proportion of non-smoking groups like healthcare workers, or exercise habits.
These, moreover, tend to only show correlation, not causation. They also do not account for patients having a tendency to lie to healthcare professionals about smoking.
Studies that check for “daily smokers” sometimes miss out on the smoking habits and histories of the participants, including those who smoke irregularly, quit recently, or have never smoked in their life. In a number of studies, the difference in mortality rates simply tends to be too drastic for it to be attributed to smoking alone.
The smoker’s paradox meanwhile shows up in sero-prevalence studies as well, because the slow immune response among smokers causes antibodies to disappear faster.