Smoking, vaping and the coronavirus (COVID-19) epidemic: rumors vs. evidence

By Dr Farsalinos

One of the main issues that many people, especially vapers, are discussing concerning the coronavirus epidemic is about the effects of e-cigarette use (and smoking) on the vulnerability to, and severity of coronavirus infection. Recently, New York City (NYC) Mayor Bill de Blasio mentioned in a news briefing that smokers of vapers are at increased risk. Miraculously, this statement was even reported by Reuters.  I wonder, what is the reason for considering valid and reporting statements made by people who have zero background on public health issues?

A link between smoking and coronavirus infection was first suggested because more men were infected than women. One (unproven) hypothesis was that this was due to the much higher prevalence of smoking among Chinese men (48.4%) than among women (1.9%). Source: Statista. A small study of just 78 patients with COVID-19-induced pneumonia was published in the Chinese Medical Journal. Of those, 67 (85.9%) showed improvement/stabilization after 2 weeks, while 11 (14.4%) showed disease progression. The study found that history of smoking was associated with 14-fold higher odds of disease progression. But there were only 5 smokers included in the study sample, and just 3 had disease progression. The data are too weak to make any recommendation. Characteristically, the odds ratio of smoking history leading to disease progression was 14.285 but the confidence intervals were huge (1.157-25.000), showing the level of uncertainty.

Another study that can be used INDIRECTLY to examine the effects of smoking was an analysis of 1099 cases published in New England Journal of Medicine. Interestingly, only 12.6% of cases were current smokers, and 1.9% were former smokers. The number is really low considering two factors:

  1. 99.1% of cases were ≥ 15 years old, thus they represent a population group that smokes tobacco cigarettes.
  2. 58.1% of cases were male.

Considering an almost 50% smoking prevalence in males, one would expect that at least 29% of the cases would be smokers (even if smoking did NOT have an adverse effect on infectivity). Thus, the reported proportion of cases being smokers is low. Of the 1099 cases, 926 were classified as non-severe (of which 11.8% were current smokers) and 173 were classified as severe (16.9% were current smokers). The primary composite end point (admission to an intensive care unit, use of mechanical ventilation, or death) occurred in 67 cases, with 25.8% being current smokers. I should emphasize that I cannot perform any multivariate analysis with this information (e.g. adjust the smoking status with for other factors such as age or the presence of other conditions such as COPD, cardiovascular disease, diabetes etc). It seems, however, that there is a low prevalence of smoking among cases, but somewhat higher prevalence of smoking among severe cases. Still, the numbers are far lower that what would be expected. Since this is an analysis of selective cases that may not be representative of the whole population of confirmed disease cases, we cannot make any definite conclusions. Still, the number of cases in the latter study is far higher than the 78 patients analyzed in the previous study.

Let’s talk about e-cigarettes now. And that is all I can say (i.e. nothing), we have zero evidence on how e-cigarette use affects coronavirus infectivity and disease progression. There is a lot of evidence that propylene glycol (one of the main ingredients in e-cigarette liquids) has anti-bacterial and anti-viral properties in aerosol form. Below is a list of studies I cited in the 2017 book on e-cigarettes that I wrote together with other colleagues:


Henle W, Zellat J. Effect of propylene glycol aerosol on air-borne virus of Influenza. Proc Soc Exper Biol Med 1941;48:544.

Robertson OH, Loosli CG, Puck TT, Bigg E, Miller BF. The protection of mice against Infection with air-borne Influenza virus by means of propylene glycol vapour. Science 1941;94:612.

Harris TH, Stokes Jr. J. The effect of propylene glycol vapour on the incidence of respiratory infections in a convalescent home for children: preliminary observations. Am J Med Sci 1942;204:430.

Harris TH, Stokes Jr. J. Air-borne cross infection in the case of the common cold: a further clinical study of the use of glycol vapours for air sterilization. Am J Med Sci 1943;200:631.

Robertson OH, Bigg E, Puck TT, Miller BF, Technical Assistance of Elizabeth A. Appell. The bactericidal action of propylene glycol vapor on microorganisms suspended in air. I. J Exp Med 1942;75:593 610.

Puck TT, Robertson OH, Lemon HM. The bactericidal action of propylene glycol vapor on microorganisms suspended in air: II. the influence of various factors on the activity of the vapor. J Exp Med 1943;78:387 406.

Let me clarify that these studies do not suggest any effect of propylene glycol on the particular coronavirus strain (COVID-19) that is linked to the global epidemic. Thus, we have no evidence on how e-cigarettes and propylene glycol use may affect disease spread and severity. Moreover, we know that the vast majority of e-cigarette users are either dual users or former smokers, so they experience the adverse effects of current and past smoking, and many may already have smoking-related disease. Thus, they may be in a higher risk group, but this is not due to e-cigarettes. Smokers switching to e-cigarettes would definitely have better prognosis (compared to continuous smoking) if smoking is found to increase infectivity and disease severity.

In conclusion, some preliminary but inconclusive evidence suggests lower prevalence of smoking among COVID-19 cases than expected (considering the smoking prevalence in the whole population) but somewhat higher rate of severity and progression of disease once the smoker is infected. But the evidence is weak and inconclusive, therefore we need to exercise caution. There is no evidence on any effects of e-cigarettes on coronavirus infectivity and disease progression, and we cannot exclude the possibility that the use of propylene glycol might have some beneficial effects. As a result, reasonable recommendations concerning smoking, e-cigarette use and the coronavirus epidemic include the following:


  1. Try to quit smoking.
  2. If you cannot quit smoking by yourself or with currently-approved methods, use e-cigarettes to quit.
  3. If you are a dual user of e-cigarettes and tobacco cigarettes, try to completely quit tobacco cigarette use.
  4. If you are a former smoker and current e-cigarette user, you may want to quit e-cigarette use but not at the risk of relapsing to smoking. You should continue to use e-cigarettes if there is any chance that quitting may lead to smoking relapse.
  5. If you have never smoked, there is no evidence that initiating e-cigarette use will prevent coronavirus infection or reduce disease severity. So, don’t start vaping.


I also URGE the medical community that has access to coronavirus cases and the virus in laboratory settings to:

  1. Record both smoking and e-cigarette use history among cases.
  2. Perform a laboratory study to examine the properties of propylene glycol exposure on COVID-19 survival.
  3. Perform a clinical trial among hospitalized cases, adding nebulized propylene glycol to the therapeutic regime.


It is sad to see that the coronavirus epidemic is being used (and abused) in the political arena. The statements reported in Reuters are not just coming from people with zero background in public health; they are coming from people who are well-known for their dogmatic, biased political stance against tobacco harm reduction and e-cigarettes. This is another example of irresponsible behavior from people who provide guidance backed by zero evidence. We should not forget the recent EVALI epidemic in the US; these people were continuously making statements about e-cigarettes causing the lung disease epidemic while this made no sense and it is now clear that EVALI was caused by illicit marijuana oils containing inappropriate ingredients. None of these people has ever publicly apologized or publicly admitted their mistake which caused so much confusion that still Americans believe that e-cigarettes, not illicit marijuana oils, were responsible for the epidemic. None seems to care about the damage in public health caused by these past statements, with many vapers relapsing to smoking and smokers being discouraged from switching to e-cigarettes based on unprecedented misinformation that was propagated by politicians.

If anyone believes that the coronavirus epidemic should be approached with the same level of irresponsibility and used in political games, then I am not at all optimistic about the future.

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