For example, the effect of health behaviors, sex hormone-mediated immune factors, and differential expression of angiotensin-converting enzyme 2 may all contribute to explaining the different prognosis of COVID-19 in men and women.25 Apart from COVID-19, men are at higher risk of serious illness from many diseases; thus, for example, men have a higher mortality rate for pneumonia, influenza, and cardiovascular disease.26 Female life expectancy has been higher than for men for all years since 1950 in most countries.27 However, the reasons for the worse prognosis in men are not well understood. Here, ACE2 is linked to pneumonia.