TMPRSS2 and COVID-19: On the other hand, low levels of androgens in women may keep at low levels TMPRSS2 expression, representing a further protective factor for the development of COVID-19 infection. Both mechanisms consistently point to the role of sex hormones and chromosomes in the differential severity of SAR-CoV2 infection between sexes, thus representing a one-way avenue to the increased susceptibility to COVID-19 in men.