the symptoms similarities between the COVID-19 and the coronavirus outbreak in 2013, wherein tobacco smoking was involved in prevalence and fatality rates (Berlin et al., 2020). Smokers, especially former smokers, may be more susceptible to 2019-nCoV and have different infection paths than non-smokers'(Cai, 2020b). These findings were replicated in the last and largest meta-analysis (including European and US data) available among peer-reviewed literature (Reddy et al., 2020). Data from low/middle-income countries are still lacking. In a retrospective case series using a Mexican nation-level dataset, current smokers were 23% less likely to be diagnosed with COVID-19 compared to non-smokers, and current smoking was not associated with adverse outcomes (Giannouchos et al., 2020). In contrast, in a large sample of Brazilians patients, smoking was associated with the risk of hospitalization and adverse outcomes (Soares et al., 2020). Smoking history may provide valuable information in identifying at-risk populations. However, to clarify this rapidly evolving topic, the smoking history should be systematically recorded in future studies on COVID-19 (Cai, 2020b).
