Various international agencies such as the World Health Organisation, and Centre for Disease Control and Prevention consider tobacco use as a risk condition associated with susceptibility to COVID 19 and progression to adverse outcomes. Vardavas and Nikitara conducted a systematic review of evidence to evaluate the association between smoking and COVID 19 outcomes. They have included a range of outcomes including disease severity, need for mechanical ventilation and intensive care hospitalisation and death. The authors’ identified five studies covering a total population of 1349 COVID 19 patients in their systematic review. Although some of the included studies suggested that smoking may be associated with adverse outcomes in COVID 19 patients, no conclusive evidence was found.
Systematic reviews are exposed to several potential biases. Firstly, the COVID 19 data are just started emerging from various parts of the world. Absence of evidence should not be construed as evidence of absence. Secondly, in emergency situations, history taking is often ignored and habits such as tobacco use never gets reported or documented in case records. Thirdly, a lot of COVID 19 related literature may be available in languages other than English and therefore restricting the publication language to English may not be ideal. Finally, the systematic reviews should be comprehensive and ideally it should cover multiple databases.
Both smoking and COVID 19 are individually known to harm cardiovascular and respiratory systems. Given the involvement of both the cardiovascular and respiratory systems in the disease progression of COVID 19, even quitting smoking for a few days may have beneficial effects. Further, smoking is often a group activity in public settings and it could further increase susceptibility for transmission of COVID 19. Therefore, quitting smoking may have additional benefits in the COVID 19 season.