Suggestion that smoking protects from COVID-19 may be dangerous to public health

A new pandemic generates anxiety and confusion and drives people to seek remedies that may have little scientific evidence of efficacy. Based upon a flawed interpretation of preliminary COVID-19 data, the hypothesis that cigarette smoking protects one from coronavirus has emerged. Some have taken these incorrect findings to an extreme, as in France, where the online sales of nicotine products online was recently banned. 

What is being overlooked is that the same data also show smokers are more likely to be admitted to the ICU, require intubation, or die from COVID-19 infection. A 2003 myth that smoking might protect against a different coronavirus that caused the SARS pandemic was later proven incorrect. The current misguided belief that smoking protects from COVID-19 infection may prove dangerous with significant negative effects on public health. 

A vital source of the confusion likely stems from a misinterpretation of early evidence from small studies in China and Europe. The argument is that the proportion of smokers observed among COVID-19 patients is lower than what might be expected based on national smoking rates. A careful review of the data instead reveals the findings are more likely due to statistical flaws and sampling error, along with poor rates of screening and documentation of smoking history by physicians.

Smoking cessation usually isn’t the primary reason for a patient visit to the emergency room, where cigarette use often isn’t discussed. Busy physicians may forget to document smoking history in admission notes if they even ask. To make up for this deficiency, respiratory therapists, pharmacists, and other smoking cessation professionals often assist in entering this information, which can become buried in the many pages of the medical record. 

There are other severe limitations in the analysis that concludes smoking protects against COVID-19. 

First, decades of research clearly show that smoking worsens outcomes from bacterial and viral cases of pneumonia and causes chronic lung disease. Smoking increases the numbers of angiotensin-converting enzyme receptors on lung cells that the coronavirus uses to infect the host and cause severe lung disease. There is no scientific basis to explain the contradiction between the proposed myth that smoking protects from contracting COVID-19, and the observed worse COVID-19 outcomes for smokers compared to non-smokers.

Second, the initial viral exposure in an outbreak is not to a broad range of the population, but instead to a limited group, resulting in sampling error. Early Chinese studies noted patients’ age, rates of smoking and demographics may not reflect the general population.

Using the national smoking rate across age groups, and not adjusting for the age of the patients, will skew the results. Many early COVID cases involved health care workers (who generally smoke at a lower rate) who treated the initial patients, and their inclusion may help explain why the proportion of smokers is lower.    

Third, some COVID-19 patients died at home or in nursing homes before reaching medical care but were excluded in these studies, which focused on milder cases. Other patients arrived at the emergency room while critically ill or already intubated, or confused. The doctors had limited time to obtain a complete smoking history, and instead likely performed an expedited history before moving to the next critically ill patient. Critical pieces of information may have been inadvertently omitted, as clinicians treat multiple patients first, and leave charting until later.

Finally, the early COVID-19 reports were rushed to press, without time for careful chart review to verify smoking status. Missing data about smoking history will results in a smoker being incorrectly recorded as a non-smoker, thus under-estimating the smoking prevalence. What is more important is that COVID-19 patients correctly identified as smokers had worse outcomes. After the pandemic is controlled, future researchers can perform follow-up to determine smoking rates more accurately.

The scientific evidence is clear that smoking harms respiratory health. A final concern with the French study is lead author Jean-Pierre Changeux’s ties to the tobacco industry, having previously accepted $220,000 from the tobacco industry-funded Council for Tobacco Research in the 1990s, and collaborated with RJ Reynolds and Philip Morris. Until we have unbiased data, supported by solid research design, and free of any tobacco industry influence, we would caution against the likely myth that smoking protects from acquiring COVID-19. More than 300,000 UK smokers may have quit due to COVID-19 fears. 

John Maa, M.D., is the past-president, at San Francisco Marin Medical Society. Bonnie Halpern-Felsher, Ph.D., is a professor of Pediatrics at Stanford University.