Smoking is associated with worse outcomes of COVID-19 particularly among younger adults: a systematic review and meta-analysis

Introduction: Smoking impairs lung immune functions and damages upper airways, increasing risks of contracting and severity of infectious diseases.

Methods: We searched PubMed for studies published from January 1-May 25, 2020. We included studies reporting smoking behavior of COVID-19 patients and progression of disease, including death. We used a random effects meta-analysis and used meta-regression and lowess regressions to examine relationships in the data.

Results: We identified 47 peer-reviewed papers with a total of 31,871 COVID-19 patients, 5,759 (18.1%) experienced disease progression and 5,734 (18.0%) with a history of smoking. Among smokers, 29.2% experienced disease progression, compared with 21.1% of non-smokers. The meta-analysis confirmed an association between smoking and COVID-19 progression (OR 1.56, 95% CI 1.32-1.83, p=0.001). Smoking was associated with increased risk of death from COVID-19 (OR 1.19, 95% CI 1.05-1.34, p=0.007). We found no significant difference (p=0.432) between the effects of smoking on COVID-19 disease progression between adjusted and unadjusted analyses, suggesting that smoking is an independent risk factor for COVID-19 disease progression. We also found the risk of having COVID-19 progression among younger adults (p=0.023), with the effect most pronounced among people under about 45 years old.

Conclusions: Smoking is an independent risk for having severe progression of COVID-19, including mortality. The effects seem to be higher among young people.

Implications: Smoking prevention and cessation should remain a priority for the public, physicians, and public health professionals during the COVID-19 pandemic.