|
| Author | Date | Studies | Conclusions | Notable limitations |
|
| Vardavas et al. | March 2020 | 5 from China | Smoking likely had a negative impact on COVID-19 disease progression and outcomes | Very small sample, very early data |
| Berlin et al. | April 2020 | 6 from China | More evidence is needed if tobacco use may be a risk factor for both transmission and negative outcomes | Small sample, early data |
| Farsalinos et al. | May 2020 | 13 from China | Smokers are underrepresented among hospitalized patients; former smokers have higher odds of adverse outcomes than current smokers; nicotine may be protective | Relies on early data exclusively from China; unadjusted for confounding factors including sociodemographic factors |
| Gulsen et al. | June 2020 | 14 from China, 2 from Italy | History of smoking is associated with severe COVID-19 | Relies heavily on early data from China; classifications of both smokers and COVID-19 patients varied |
| Patanavanich et al. | Sept 2020, preprint | 47 from 16 countries | Smoking is an independent risk factor for COVID-19 severity and death | Does not include research published after May 25, 2020; includes studies with very small (>0) smoking populations; no requirement regarding COVID-19 diagnosis |
| Salah et al. | Oct 2020 | 10 from various countries (China, UK, Thailand) | Smoking doubles the risk of mortality in COVID-19 patients | Used only PubMed; included mortality as an outcome |
| Gupta et al. | Nov 2020 | 23 from various countries (China, US, Italy) | Tobacco use is associated with comorbidities which increase the likelihood of negative COVID-19 outcomes | Literature review; not systematic |
| Umnuaypornlert et al. | Feb 2021 | 40 from 8 countries | Tobacco use increases the risk of disease severity and death in COVID-19 patients | No requirement regarding COVID-19 as diagnosis; no minimum number of smokers to be included in studies |
|
