Factors related to asymptomatic or severe COVID-19 infection.

The factors that may contribute to a COVID-19 patient remaining in the asymptomatic stage, or to the infection evolving into the more serious stages are examined. In particular, we refer to the TMPRSS2 expression profile, balance of androgen and estrogen, blood group-A and/or B, nonsynonymous mutations in ORF3, and proteins NS7b and NS8 in SARS-CoV-2. Also, we review other factors related to the susceptibility and pathogenicity of SARS-CoV-2.