Study on Safety and Efficacy of Two Doses of PRS CK STORM in the Modulation of the Cytokine Storm in Patients With Acute Respiratory Infection Caused by SARS-Cov-2, Influenza A, Influenza B and Respiratory Syncytial Virus (RSV)

This is a double-blind, randomized, phase I/II pilot clinical trial of two doses of PRS CK STORM in adult participants with SIRS caused by SARS-Cov-2, influenza A, influenza B and RSV All participants will receive the standard of care for SIRS, according to its viral origin: * Clinical management of COVID-19: hospital care (Centro de Coordinación de Alertas y Emergencias Sanitarias, 2020). * Clinical practice guidelines for influenza (WHO, 2024). Participants who meet the eligibility criteria will be randomized in blocks to reach the 2:2:1 ratio (dose A: dose B: placebo). This study consists of two parts: Part 1: Doses A and B of PRS CK STORM will be evaluated in 2 groups of 4 participants (3:1; PRS CK STORM: placebo). It starts with a first sentinel group of 4 participants who will be assigned to placebo or study drug dose A. First, only 2 participants will randomly be assigned to receive the active treatment of dose A or placebo for 5 consecutive days. These 2 first participants will be followed up to 48h after the last drug administration (short-term safety follow-up period) when a safety assessment will be completed before treating the other 2 participants in this group. If the study drug is considered safe during the short-term safety assessment planned 48h after the last drug administration, then 2 additional participants will be treated with dose A for 5 consecutive days to complete the first sentinel group of 4 participants. These 2 participants will be followed up to 48h after the last study drug administration before moving to dose B. After the assessment of data collected follow-up for this first group, a second small sentinel group of other 4 participants will be treated with a higher dosage (dose B) following the same process, as long as dose A has been considered safe. First, only 2 participants will randomly receive the active treatment of dose B or placebo for 5 consecutive days and then these 2 first participants will be followed up to 48h after the last drug administration when a safety assessment will be completed before treating the other 2 participants in this group. If the study drug is considered safe during the safety assessment planned 48h after last drug administration, then two additional participants will be treated with dose B for 5 consecutive days to complete the sentinel second group of 4 participants evaluating dose B. These 2 participants will be also followed up to 48h after the last study drug administration when a safety assessment will be completed before treating the other 2 participants in this group. All these 8 participants included in Part 1 will continue in a long-term safety follow-up period until 1 year post treatment. Part 2: 42 additional participants will be treated for 5 consecutive days. These 42 participants will be randomized to three treatment arms: 17 in the active arm with dose A, 17 participants in the active arm with dose B and 8 participants in the placebo arm. All participants in Part 2 will be followed up to 48h after the last study drug (short-term safety follow-up period). Once all participants treated in Part 2 finished the short-term safety follow-up period (48h after last study drug administration), all data will be verified and statistically analyzed in an interim analysis. All participants will be followed up to 1 year post treatment (long-term safety follow-up period). Therefore, considering the participants enrolled in Part 1 and Part 2 the total number of participants for safety, tolerability and efficacy analysis will be 50 assigned to three different arms (total randomization ratio 2:2:1), 20 participants will be assigned to dose A, 20 participants will be assigned to dose B and 10 participants will be assigned to placebo. To sum up, considering the participants enrolled in Part 1 and Part 2 the total number of participants for safety, tolerability and efficacy analysis will be 50 assigned to three different arms (total randomization ratio 2:2:1), 20 participants will be assigned to dose A of PRS CK STORM, 20 participants will be assigned to dose B of PRS CK STORM and 10 participants will be assigned to placebo. The estimated duration of the study for individual participants will be 12 months (screening: 3 days, treatment period: 5 days, short-term safety follow-up period: 2 days after the last drug intake and long-term safety follow-up period: up to 48 weeks from randomization). It is hypothesized that both doses of PRS CK STORM for intravenous administration are safe, well tolerated and clinically beneficial versus placebo for participants with SIRS-associated cytokine storm.