dcyphr | Smoking is Associated with COVID-19 Progression: A Meta-Analysis


Objective: To determine the association between smoking and progression of COVID-19.

Design: A meta-analysis of 12 published papers.

Data Source: PubMed database was searched on April 6, 2020.

Eligibility criteria and data analysis: The authors included studies reporting smoking behaviour of COVID-19 patients and progression of disease. 

Main Outcome Measures: The study outcome was progression of COVID-19 among people who already had the disease.

Results: The authors identified 12 papers with a total of 9,025 COVID-19 patients. 495 patients had a history of smoking. The analysis showed association between smoking and COVID-19. Limitations in the papers suggest that the actual risk of smoking may be higher.

Conclusions: Smoking is a risk factor for COVID-19. Health professionals should collect data on smoking as part of clinical management.


COVID-19 is a pandemic. Smoking increases the risk of infections as it damages the upper airways. The authors reviewed and summarized 12 papers presenting data on the association between COVID-19 and smoking.


PubMed database was searched on April 6, 2020. 12 relevant studies were identified. The researchers compared disease progression in smokers and non-smokers in these 12 studies. 


9025 patients were investigated. 878 patients had disease progression. 495 patients had a history of smoking. 88 patients with smoking history had disease progression. This was a higher percentage than that of non-smokers.

The analysis showed a relation between smoking and COVID-19 progression.


This analysis confirms that smoking is a risk factor for COVID-19. Smokers have 2.25 times risk of severe COVID-19 outcomes compared to never-smokers. This is unsurprising due to the adverse effects of smoking on the body.

The study has several limitations. The definition of smoking was not consistent. Only 3 studies differentiated between current smokers and former smokers. Since the lung can recover in former smokers, the data is somewhat biased. 

The smoking prevalence in the studies was lower than the population in general. This means that some smokers may have been identified as non-smokers. This increase bias in the study.

None of these studies investigated e-cigarettes. 

These limitations suggest that the risk of smoking has been underestimated. All 12 studies investigated people who already had the disease. This means that the study does not investigate the risk of getting COVID-19 but the risk of COVID-19 becoming severe. 

As disease testing increases, it would be useful to collect data on smoking.


Smoking is associated with COVID-19 progressions. Health professionals should collect data on smoking. They should also advice the public to stop smoking to reduce the pandemic spread.