TMPRSS2 and COVID-19: Age and subsequent changes in sex hormones (estrogen, progesterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH)), especially in women during their physiological situations (puberty, menstruation, and menopause), and sex (sex chromosome types X or Y, the encoding of immune system-related genes from chromosome X, the high expression of the ACE-2 receptor, the low expression of TMPRSS-2 from chromosome X, the high level of testosterone, the decreased expression of ACE-2, and the elevated level of TMPRSS-2 in men) are the important, impressive factors in COVID-19 (9).