Convalescent Plasma for COVID-19

The purpose of this proof of concept study is to provide COVID-19 convalescent plasma to patients with moderate to severe COVID-19 and assess: * the titer of anti-COVID-19 antibodies in the donors and in the patients before and after treatment; * the in-depth analysis of immunological parameters in the donors and in recipient before and after treatment; * the impact of plasma transfusion on the reduction of viral load and inflammation * safety and tolerability * clinical efficacy