ACE2 and COVID-19: Both COVID-19 naïve controls and COVID-19 convalescents show a shift towards higher antibody titers and more binding inhibition after the second vaccine dose and the booster dose, respectively (Fig. 1); however after 6 months ACE2 binding inhibition almost completely disappeared despite still elevated antibody titers in dually vaccinated COVID-19 naïve subjects, whereas among boosted convalescents ACE2 binding inhibition was much better preserved (Fig. 3).