Smoking may worsen COVID-19 severity

Smoking appears to contribute to a more severe COVID-19*, leading to more adverse outcomes and negative disease progression, according to a recent systematic review.

“[W]e conducted a systematic review of studies on COVID-19 that included information on patients’ smoking status to evaluate the association between smoking and COVID-19 outcomes, including the severity of the disease, the need for mechanical ventilation, the need for intensive care unit (ICU) hospitalization and death,” said researchers.

Accessing the databases of PubMed and Science Direct, the team retrieved five eligible studies. All were conducted in China and were either retrospective or prospective in design. Sample sizes ranged from 41 to 1,099 COVID-19 patients. All studies had been conducted during the first 2 months of the pandemic. [Tob Induc Dis 2020;18:20]

In the largest study (n=1,099), COVID-19 was largely nonsevere, mirroring currently known trends of the disease presentation. Among the 173 patients who suffered from severe symptoms, 16.9 percent were current smokers and 5.2 percent were former smokers.

In patients who needed mechanical ventilation, were admitted to the intensive care or died, more than a quarter were currently smoking, while 7.6 percent were formerly hooked on the habit.

In contrast, 11.8 percent and 1.3 percent of the nonsevere subgroup were current and former smokers, respectively. Corresponding rates of smoking status were 11.8 percent and 1.6 percent in patients with less adverse outcomes. This study did not present statistical analyses.

In a smaller study (n=78), smoking was significantly more common among patients who had worse COVID-19 outcomes than in those who improved or stabilized (27.3 percent vs 3.0 percent; p=0.018). This was supported by multivariable logistic regression analysis, which identified smoking history as a significant risk factor (odds ratio, 14.28, 95 percent confidence interval, 1.58–25.00; p=0.018).

This, however, was not reflected in the three remaining studies, which showed that smoking, whether current or past, was generally associated with only a nominal increase in the likelihood of worse COVID-19, without achieving statistical significance.

“COVID-19 is a coronavirus outbreak that initially appeared in Wuhan, Hubei Province, China, in December 2019, but it has already evolved into a pandemic spreading rapidly worldwide,” the researcher said. However, as the situation continues to evolve, data regarding clinical characteristics and prognostic factors remain limited. [New Engl J Med 2020;doi:10.1056/NEJMoa2001316]

Smoking is of special interest, given its proven detrimental effects on lung health and respiratory diseases and on the immune system. [Tob Induc Dis 2019;17:72; Tob Induc Dis 2016;14:35]

“Although further research is warranted as the weight of the evidence increases, with the limited available data, and although the above results are unadjusted for other factors that may impact disease progression, smoking is most likely associated with the negative progression and adverse outcomes of COVID-19,” the researchers said.

*Coronavirus disease 2019