I take it as a slight badge of honour that an article I wrote in the early days of Covid was flagged as fake news on Facebook. I wrote a follow up to the offending article for Spiked two weeks ago titled 'The great Covid and fags cover up'. Regular readers will know what I'm talking about. If you don't, hit the link.
The article includes links to Snowdon's blog, where he has compiled a list of studies (including those published by reputed medical journals such as Lancet and Nature), and claims that an overwhelming “87 percent” of the studies acknowledge that smokers are typically less likely to catch the virus and be hospitalized.
On reviewing the exhaustive list of studies that Snowdon refers to, Logically found that several of them are pre-prints rather than peer-reviewed published papers.
In his article, Snowdon argued that search results for COVID-19 and tobacco/smoking lead to WHO briefs and articles in publications such as the British Medical Journal (BMJ). He claims that these studies merely state that smokers are at greater risk without addressing the actual findings of the studies that suggest smokers had a reduced risk of contracting COVID-19.
In an article published in The Lancet on August 16, 2022, Professor John Griggs, a respiratory and environmental medicine specialist, acknowledged that there were studies in the early stages of the pandemic that appeared to provide evidence that smoking might protect against COVID-19. However, he also noted that during those early stages of the pandemic, "scientific journals rightly responded to the SARS-CoV-2 pandemic by more rapidly publishing their COVID-19 research”.
Prof. Griggs also cited a more detailed article published in The Lancet, which examined epidemiological studies of tobacco use and COVID-19, and found that the studies have produced conflicting results, meaning further research is needed before one can claim that smoking affects susceptibility to the virus. The article nonetheless concludes that "the evidence indicates that smokers are at greater risk of poor outcomes from COVID-19, including hospital admission and progression to severe disease than are non-smokers."
...not a formal systematic review and based largely on searches up to August 2021
We identified conflicting evidence for the effects of cigarette smoking on the incidence of SARS-CoV-2 infection (appendix pp 3–6). Specifically, we identified 12 multivariable and eight univariate or frequency-reporting studies that found a positive effect of cigarette smoking on SARS-CoV-2 infection rates, and 14 multivariable and 12 univariate or frequency-reporting studies that found a negative effect.
Albiges et al. didn't look at infections, it looked at mortality risk.
Li et al. is the same study mentioned above; an ecological study about vaping, not smoking.
Dev et al. found an association between smoking and infection but this disappeared after adjustment. I'm happy to include this study in the list as supporting the null hypothesis.
Similarly, Mostafa et al. found associations with both former and current smoking which disappeared after adjustment for confounding factors. I'll add this one as a null finding too.
Unless we think epidemiological findings are more robust before they are adjusted for exogenous variables, none of these studies support Benowitz's argument. And none of the 'frequency-reporting studies' are relevant at all (I won't list them but feel free to check them yourself).
Benowitz also cites five studies which, he says, support the null hypothesis, i.e. they find no association either way. They are...
Liu et al. did not look at infection although it did find that smoking was not associated with Covid mortality risk.
Zhu et al. looked at hospitalisations, not infections.
Dadgari et al. is a study from Iran which does indeed support the null hypothesis. I'll add it to the list.
Dayem et al. is a study from England which doesn't give relative risks for smoking but does say that 'current smoking status appeared to have a protective effect in our cohort after adjusting for comorbidities, as has been observed by others'.
Finally, Benowitz lists 14 studies using multivariate analyysis which show a protective effect from smoking, plus six using univariate analysis. Some of them are on my list already and a few of them don't meet my criteria, but there are eight studies that I've missed. They are...
Ghinai et al. is a study of homeless people in Chicago which found that smokers were less likely to be infected (0.71; 95% CI, 0.60-0.85).
Gu et al. is a US study which found: 'Being a current smoker (self-reported in the latest EHR encounter) was associated with a reduced chance of having positive test results (OR, 0.31 [95% CI, 0.20-0.48]; P < .001).'
Vila-Córcoles et al. is a study from Spain which found smokers 57% less likely to be infected (0.43 (0.25-0.74)).
Fernandez-Fuertes et al., is a study from Spain involving HIV patients. It found that 'active tobacco smoking was the only factor independently associated with lower risk of SARS-Cov-2 infection [Incidence rate ratio: 0.29 (95% CI 0.16–0.55)'.
Green et al. is a study from Israel involving patients with bronchial asthma which found: 'A significantly higher proportion of smokers was observed in the COVID-19–negative group than in the COVID-19–positive group (4734 [13.45%] vs 103 [4.55%]; P < .001).'
Gu et al. is a study from Michigan which found that smokers were much less likely to test positive for COVID-19 (0.31 (0.20-0.48)).
Lombardi et al. is a seroprevalence survey of Italian healthcare workers which found smokers were 59% less likely to test positive (0.41 (0.27-0.61)).
Holuka et al. is a study from Luxembourg which found smokers half as likely to test positive for COVID-19 (0.50 (0.30–0.83)).
These eight, plus the four studies that reached different conclusions, mean that we have an extra twelve studies to add. So let's get rid of the four pre-prints, two of which use the Biobank data. If they were going to be published in journals, they probably would have been by now. I've also taken a couple of studies out of the list, like this one, which are interesting but don't quite fit my criteria. I kept the Mendelian Randomisation studies even though they don't really fit the criteria because they're virtually the only studies that find an increased infection risk from smoking.
The new list is here. It has a grand total of 105 epidemiological studies looking at the relative risk of SARS-CoV-2 infection among current smokers.
Of the 105 studies, 90 find a statistically significant reduction in risk of infection from SARS-C0V-2 among current smokers.
Eight of them find no statistically significant association either way (although theyy are nearly all below 1.0).
Four of them find an increase in risk.
Three of them found mixed results.
I mean, I guess you could say that these studies are 'conflicting' but there's a pretty clear tendency in one direction, isn't there?
The WHO, in an updated 2020 review, which excluded the non-peer-reviewed reports and pre-prints, found that smoking is associated with increased severity of disease and death in hospitalized COVID-19 patients. However, it could not quantify the risk to smokers of infection by SARS-CoV-2 or hospitalization for COVID-19. The brief said that more population studies are needed to address these questions
Even if we ignore the fact that the WHO is corrupt and incompetent, the important thing to note is that this was a '2020 review'. More
population studies have been conducted in the last two and half years and they overwhelmingly point to a protective effect. Perhaps this explains why the WHO haven't updated their webpage?
Logically also contacted Dr. Satyanarayana Mysore, head of the pulmonology department at Manipal Hospitals in Bengaluru, to get more clarity on the matter. Dr Mysore dismissed the claim that smokers are less likely to catch COVID-19, and said that there are major limitations in the studies associating smoking with with reduced risk of getting COVID-19. He noted that WHO has listed smoking and chronic obstructive pulmonary disease (COPD) as major risk factors for COVID-19. He added that smoking does not protect anyone from COVID-19 and has the potential to harm.
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