Contribution of tobacco smoking to the risk of novel coronavirus infection and related mechanisms

The severe acute respiratory syndrome coronavirus 2 （SARS-CoV-2） and its variants are still globally spreading. Vaccines can reduce the mortality， but cannot eliminate the risk of infection. The identification and protection of the high-risk susceptible population remains of great importance for the prevention and control of SARS-CoV2 and other coronavirus infections. Smoking is an important risk factor for many respiratory diseases， and therefore may also influence the risk of SARS-CoV2 infection and the disease progression after infection. This study reviewed the epidemiological and mechanistic evidence supporting the relationship between tobacco exposure and SARS-CoV2 infection， summarized the contributing effects of tobacco exposure to the infection risk， disease severity， and mortality of COVID-19， and analyzed the molecular mechanisms by which cigarette smoking affects COVID-19 through regulating inflammatory microenvironment and gene expression.