Reports of the use of plasma from convalescent patients and purified immunoglobulin preparations in respiratory infections by various viral agents and SARS-CoV-2 in severely ill patients suggest that specific neutralizing antibodies may benefit their clinical course. During the previous SARS-CoV epidemic in 2003, preparations of hyperimmune equine serum were produced and demonstrated in vitro viral neutralization. These preparations were also successful in several animal models. Taking advantage of the important trajectory of our country in the study and use of equine hyperimmune serums with neutralizing antibodies for snake venom, preparations of hyperimmune serums against recombinant proteins of SARS-CoV-2 were produced through repeated immunization of horses, a first group of animals was inoculated with the "S" (Spike) protein of the virus and the second group with a mixture "M" of the S1 (Spike) proteins, the N (Nucleoprotein) protein and a construct with epitopes of the S1, E (Envelope) and M (Membrane) proteins, generating two different pharmaceutical preparations.

Objective: Evaluate the efficacy and safety of two hyperimmune equine serum anti-Sars-CoV-2 ("S" and "M") formulations as an addition to the standard therapeutic approach for hospitalized patients with COVID-19 over 18 years of age with the presence of at least 2 risk factors and a symptom onset period not exceeding 10 days.

A total of 52 patients will be included and randomly divided into two balanced groups. On day 1, all participants from each group will receive an intravenous infusion containing 10ml (one vial) of hyperimmune equine anti-Sars-CoV-2 serum labeled as A or B.

Patients will be evaluated clinically, general laboratory, SARS-CoV-2 serologies, SARS-CoV-2 viral load and cytokines level as well as pulmonary ultrasound. Data will be collected for both groups on Days 0 to 7, 10 and 14 or discharge after completion of treatment. The study will end for each participant on the day of discharge from the hospital.

Inclusion Criteria:

• Agreement to participate in the study by signing the prior informed consent.
• Age over 18 years.
• Inpatient with RT-PCR confirmation of SARS-CoV-2.
• Period of onset of symptoms related to COVID-19 not greater than 10 days
• Presence of at least 2 documented risk factors
• Moderate and severe clinical presentation of the disease.

Exclusion Criteria:

• Patients who did not sign the Informed Consent.
• Critical patient.
• Patient previously bitten by a snake that was treated with equine hyperimmune serum.
• Patients with COVID-19 on an outpatient basis.
• Pregnant women.
• Patients in Hemodialysis program.
• Patients who have already received plasma from a convalescent COVID-19 patient.
• Patients who were classified prior to the diagnosis of COVID-19 by the treating physician as having a reserved prognosis with a short lifespan.