The issue of tobacco smoking and risk for acute respiratory infection has become a talking point amid the Covid-19 pandemic. According to a paper published in The Lancet journal, robust evidence suggests that several mechanisms may increase the risk of respiratory tract infections in smokers. Smoking impairs the immune system and the ability to contain infection. The risk of contracting pneumonia is about 3–5 times higher in smokers and they are also 5-times more likely to contract influenza, states the paper. There's not enough evidence to support that tobacco smoking increases the risk of being infected by Covid-19. However, available studies indicate that current smokers have increased gene expression of ACE2 - the main receptor used by the Covid-19 virus to gain entry to host cells and cause active infection. The challenge for Covid-19 studies is to have large enough sample sizes with all variables that might be associated with tobacco smoking and health.