group a - yellow fever any clinically significant medical condition or medical history that, in the opinion of the investigator or sponsor, would interfere with the subject's ability to participate in the study or increase the risk of participation for that subject employment by the study site, or an immediate family relationship to either study site employees or sponsor employee lack of suitable veins for venipuncture/cannulation as assessed by the investigator at screening participation in any other investigational drug or vaccine study currently or within the past 30 days diagnosis of yf vaccine-related viscerotropic disease subjects with hepatic encephalopathy as defined by conn score ≥ 1. subject has severe immunosuppression or immunodeficiency, leukemia, lymphoma, thymic disease, generalized malignancy, or radiation therapy (within the past 3 months), or is undergoing current treatment with immunosuppressive drugs, defined as drugs that impair immune responses to infections a treatment plan for yf that would include concomitant administration of antiviral medications inclusion criteria group b - covid-19 ability to provide written informed consent, accept randomization to any assigned treatment arm, and comply with planned study procedures males and nonpregnant, non-breast-feeding females, aged 18 years or older male and female subjects must agree to the contraception requirements and must meet the inclusion criteria regarding contraception as outlined in the protocol subject weight ≥ 50 kg (110 lb.) clinical syndrome consistent with moderate-severe (but not critically ill) covid-19, defined by at least one of the following: symptoms of acute viral lower respiratory tract infection, such as fever, non-productive cough, dyspnea, and either 1) a pulse oximetry oxygen saturation (spo2) ≤ 94% or a respiratory rate > 24 breaths/minute as measured at rest without use of supplemental oxygen or 2) a clinical requirement for supplemental oxygen treatment or non-invasive mechanical ventilation radiographic pulmonary findings seen on chest imaging (chest x-ray or computed tomography [ct scan]) consistent with covid-19 positive test for sars-cov-2 by molecular amplification of the virus in a respiratory specimen (nasopharyngeal, oropharyngeal, lower respiratory tract [eg, expectorated sputum]) collected < 96 hours prior to randomization. note: subjects may have a positive test recorded prior to screening if they are admitted to the hospital with a presumed case of covid-19

group a - yellow fever any clinically significant medical condition or medical history that, in the opinion of the investigator or sponsor, would interfere with the subject's ability to participate in the study or increase the risk of participation for that subject employment by the study site, or an immediate family relationship to either study site employees or sponsor employee lack of suitable veins for venipuncture/cannulation as assessed by the investigator at screening participation in any other investigational drug or vaccine study currently or within the past 30 days diagnosis of yf vaccine-related viscerotropic disease subjects with hepatic encephalopathy as defined by conn score ≥ 1. subject has severe immunosuppression or immunodeficiency, leukemia, lymphoma, thymic disease, generalized malignancy, or radiation therapy (within the past 3 months), or is undergoing current treatment with immunosuppressive drugs, defined as drugs that impair immune responses to infections a treatment plan for yf that would include concomitant administration of antiviral medications inclusion criteria group b - covid-19 ability to provide written informed consent, accept randomization to any assigned treatment arm, and comply with planned study procedures males and nonpregnant, non-breast-feeding females, aged 18 years or older male and female subjects must agree to the contraception requirements and must meet the inclusion criteria regarding contraception as outlined in the protocol subject weight ≥ 50 kg (110 lb.) clinical syndrome consistent with moderate-severe (but not critically ill) covid-19, defined by at least one of the following: symptoms of acute viral lower respiratory tract infection, such as fever, non-productive cough, dyspnea, and either 1) a pulse oximetry oxygen saturation (spo2) ≤ 94% or a respiratory rate > 24 breaths/minute as measured at rest without use of supplemental oxygen or 2) a clinical requirement for supplemental oxygen treatment or non-invasive mechanical ventilation radiographic pulmonary findings seen on chest imaging (chest x-ray or computed tomography [ct scan]) consistent with covid-19 positive test for sars-cov-2 by molecular amplification of the virus in a respiratory specimen (nasopharyngeal, oropharyngeal, lower respiratory tract [eg, expectorated sputum]) collected < 96 hours prior to randomization. note: subjects may have a positive test recorded prior to screening if they are admitted to the hospital with a presumed case of covid-19

group a - yellow fever - any clinically significant medical condition or medical history that, in the opinion of the investigator or sponsor, would interfere with the subject's ability to participate in the study or increase the risk of participation for that subject - employment by the study site, or an immediate family relationship to either study site employees or sponsor employee - lack of suitable veins for venipuncture/cannulation as assessed by the investigator at screening - participation in any other investigational drug or vaccine study currently or within the past 30 days - diagnosis of yf vaccine-related viscerotropic disease - subjects with hepatic encephalopathy as defined by conn score ≥ 1. - subject has severe immunosuppression or immunodeficiency, leukemia, lymphoma, thymic disease, generalized malignancy, or radiation therapy (within the past 3 months), or is undergoing current treatment with immunosuppressive drugs, defined as drugs that impair immune responses to infections - a treatment plan for yf that would include concomitant administration of antiviral medications inclusion criteria group b - covid-19 - ability to provide written informed consent, accept randomization to any assigned treatment arm, and comply with planned study procedures - males and nonpregnant, non-breast-feeding females, aged 18 years or older - male and female subjects must agree to the contraception requirements and must meet the inclusion criteria regarding contraception as outlined in the protocol - subject weight ≥ 50 kg (110 lb.) - clinical syndrome consistent with moderate-severe (but not critically ill) covid-19, defined by at least one of the following: 1. symptoms of acute viral lower respiratory tract infection, such as fever, non-productive cough, dyspnea, and either 1) a pulse oximetry oxygen saturation (spo2) ≤ 94% or a respiratory rate > 24 breaths/minute as measured at rest without use of supplemental oxygen or 2) a clinical requirement for supplemental oxygen treatment or non-invasive mechanical ventilation 2. radiographic pulmonary findings seen on chest imaging (chest x-ray or computed tomography [ct scan]) consistent with covid-19 - positive test for sars-cov-2 by molecular amplification of the virus in a respiratory specimen (nasopharyngeal, oropharyngeal, lower respiratory tract [eg, expectorated sputum]) collected < 96 hours prior to randomization. note: subjects may have a positive test recorded prior to screening if they are admitted to the hospital with a presumed case of covid-19

group a - yellow fever - any clinically significant medical condition or medical history that, in the opinion of the investigator or sponsor, would interfere with the subject's ability to participate in the study or increase the risk of participation for that subject - employment by the study site, or an immediate family relationship to either study site employees or sponsor employee - lack of suitable veins for venipuncture/cannulation as assessed by the investigator at screening - participation in any other investigational drug or vaccine study currently or within the past 30 days - diagnosis of yf vaccine-related viscerotropic disease - subjects with hepatic encephalopathy as defined by conn score ≥ 1. - subject has severe immunosuppression or immunodeficiency, leukemia, lymphoma, thymic disease, generalized malignancy, or radiation therapy (within the past 3 months), or is undergoing current treatment with immunosuppressive drugs, defined as drugs that impair immune responses to infections - a treatment plan for yf that would include concomitant administration of antiviral medications inclusion criteria group b - covid-19 - ability to provide written informed consent, accept randomization to any assigned treatment arm, and comply with planned study procedures - males and nonpregnant, non-breast-feeding females, aged 18 years or older - male and female subjects must agree to the contraception requirements and must meet the inclusion criteria regarding contraception as outlined in the protocol - subject weight ≥ 50 kg (110 lb.) - clinical syndrome consistent with moderate-severe (but not critically ill) covid-19, defined by at least one of the following: 1. symptoms of acute viral lower respiratory tract infection, such as fever, non-productive cough, dyspnea, and either 1) a pulse oximetry oxygen saturation (spo2) ≤ 94% or a respiratory rate > 24 breaths/minute as measured at rest without use of supplemental oxygen or 2) a clinical requirement for supplemental oxygen treatment or non-invasive mechanical ventilation 2. radiographic pulmonary findings seen on chest imaging (chest x-ray or computed tomography [ct scan]) consistent with covid-19 - positive test for sars-cov-2 by molecular amplification of the virus in a respiratory specimen (nasopharyngeal, oropharyngeal, lower respiratory tract [eg, expectorated sputum]) collected < 96 hours prior to randomization. note: subjects may have a positive test recorded prior to screening if they are admitted to the hospital with a presumed case of covid-19