Inclusion Criteria:  Patients older than 18 years and younger than 80 years. Hospitalized for COVID-19 at the "Escuela Hogar" Hospital in Corrientes, Argentina from September 2020 to April 2021. Confirmed diagnosis of COVID-19 by SARS-CoV-2 Antigen Test or qualitative reverse transcriptase-polymerase chain reaction (qRT-PCR -GeneoDX Co, Ltd or similar) or Dosage of anti-SARS-CoV-2 IgG / IgM antibodies Who received hyperimmune anti-SARS-CoV-2 serum according to the indication approved by ANMAT for use after the approval date (January 2021 to April 2021) or Patients with the same indication corresponding to the period prior to the approval date (September 2020 to January 2020) With severe disease defined as individuals with tachypnea> 30 breaths per minute or oxygen saturation <94% ambient air or PaO2 / FiO2 <300, or pulmonary infiltrates> 50% on chest image.  Exclusion Criteria:  Asymptomatic disease (individuals with a positive test for SARS-CoV-2, but who do not have symptoms), mild (individuals who have compatible symptoms, but without dyspnea and with a normal chest imaging study), moderate (individuals with evidence of lower respiratory tract disease on clinical or imaging evaluation, and oxygen saturation> = 94% room air) or critical (those with respiratory failure, septic shock, and / or multi-organ dysfunction). Patients who received anti-SARS-CoV-2 hyperimmune serum off-label approved by ANMAT for use according to Regulation 9175/20. Pregnant women. Lactating women. Patients who are on mechanical ventilation or admitted to the ICU at hospital admission. Confirmation of another concomitant microbiological cause of pneumonia other than COVID-19