* persons with any clinical sign or symptoms suggestive of severe systemic illness with covid-19, including the following: 1. shortness of breath at rest, 2. resting pulse ≥125 beats per minute, 3. resting respiratory rate ≥30 breaths per minute, or 4. spo2 ≤ 93% on room air at sea level. * subjects who experienced a previous episode of acute upper respiratory tract infection, otitis, bronchitis or sinusitis or received antibiotics for these conditions within two weeks prior to and including study day 1. * severely immunodeficient persons including: 1. subjects with immunologic disorders or receiving immunosuppressive therapy (e.g., for organ or bone marrow transplants, immunomodulatory therapies for certain autoimmune diseases) 2. subjects with untreated human immunodeficiency virus (hiv) infection or treated human immunodeficiency virus (hiv) infection with a cd4 count below 350 cells/mm3 in the last six months 3. subjects actively undergoing systemic chemotherapy or radiotherapy treatment for malignancy 4. subjects using steroids as maintenance therapy for chronic conditions * subjects with active respiratory allergies or subjects expected to require anti- allergy medications during the study period for respiratory allergies. * females of childbearing potential who are either pregnant or sexually active without the use of birth control. female subjects of child-bearing potential that are sexually active must have a negative baseline pregnancy test and must agree to continue an acceptable method of birth control for the duration of the study and for 1 month post-treatment. a double barrier method, oral birth control pills administered for at least 2 monthly cycles prior to study drug administration, an intrauterine device (iud), or medroxyprogesterone acetate administered intramuscularly for a minimum of one month prior to study drug administration are acceptable methods of birth control for inclusion into the study. female subjects are considered of childbearing potential unless they are postmenopausal (absence of menstrual bleeding for 1 year - or 6 months if laboratory confirmation of hormonal status), or have had a hysterectomy, bilateral tubular ligation or bilateral oophorectomy. * subjects with a history of covid-19 or known to have developed anti-sars- cov-2 antibodies. * subjects residing in the same household with another subject participating in the study. * treatment with any investigational drug or vaccine therapy within 30 days prior to screening and willing to avoid them during the course of the study. * receipt of any dose of nitazoxanide within seven days prior to screening. * known sensitivity to nitazoxanide or any of the excipients comprising the study medication. * subjects unable to swallow oral tablets or capsules. * subjects with known severe heart, lung, neurological or other systemic disease that the investigator believes could preclude safe participation. * subjects likely or expected to require hospitalization unrelated to covid-19 during the study period. * subjects taking medications considered to be major cyp2c8 substrates. * subjects who, in the judgment of the investigator, will be unlikely to comply with the requirements of this protocol including completion of the subject diary.

* persons with any clinical sign or symptoms suggestive of severe systemic illness with covid-19, including the following: 1. shortness of breath at rest, 2. resting pulse ≥125 beats per minute, 3. resting respiratory rate ≥30 breaths per minute, or 4. spo2 ≤ 93% on room air at sea level. * subjects who experienced a previous episode of acute upper respiratory tract infection, otitis, bronchitis or sinusitis or received antibiotics for these conditions within two weeks prior to and including study day 1. * severely immunodeficient persons including: 1. subjects with immunologic disorders or receiving immunosuppressive therapy (e.g., for organ or bone marrow transplants, immunomodulatory therapies for certain autoimmune diseases) 2. subjects with untreated human immunodeficiency virus (hiv) infection or treated human immunodeficiency virus (hiv) infection with a cd4 count below 350 cells/mm3 in the last six months 3. subjects actively undergoing systemic chemotherapy or radiotherapy treatment for malignancy 4. subjects using steroids as maintenance therapy for chronic conditions * subjects with active respiratory allergies or subjects expected to require anti- allergy medications during the study period for respiratory allergies. * females of childbearing potential who are either pregnant or sexually active without the use of birth control. female subjects of child-bearing potential that are sexually active must have a negative baseline pregnancy test and must agree to continue an acceptable method of birth control for the duration of the study and for 1 month post-treatment. a double barrier method, oral birth control pills administered for at least 2 monthly cycles prior to study drug administration, an intrauterine device (iud), or medroxyprogesterone acetate administered intramuscularly for a minimum of one month prior to study drug administration are acceptable methods of birth control for inclusion into the study. female subjects are considered of childbearing potential unless they are postmenopausal (absence of menstrual bleeding for 1 year - or 6 months if laboratory confirmation of hormonal status), or have had a hysterectomy, bilateral tubular ligation or bilateral oophorectomy. * subjects with a history of covid-19 or known to have developed anti-sars- cov-2 antibodies. * subjects residing in the same household with another subject participating in the study. * treatment with any investigational drug or vaccine therapy within 30 days prior to screening and willing to avoid them during the course of the study. * receipt of any dose of nitazoxanide within seven days prior to screening. * known sensitivity to nitazoxanide or any of the excipients comprising the study medication. * subjects unable to swallow oral tablets or capsules. * subjects with known severe heart, lung, neurological or other systemic disease that the investigator believes could preclude safe participation. * subjects likely or expected to require hospitalization unrelated to covid-19 during the study period. * subjects taking medications considered to be major cyp2c8 substrates. * subjects who, in the judgment of the investigator, will be unlikely to comply with the requirements of this protocol including completion of the subject diary.

persons with any clinical sign or symptoms suggestive of severe systemic illness with covid-19, including the following: shortness of breath at rest, resting pulse ≥125 beats per minute, resting respiratory rate ≥30 breaths per minute, or spo2 ≤ 93% on room air at sea level. subjects who experienced a previous episode of acute upper respiratory tract infection, otitis, bronchitis or sinusitis or received antibiotics for these conditions within two weeks prior to and including study day 1. severely immunodeficient persons including: subjects with immunologic disorders or receiving immunosuppressive therapy (e.g., for organ or bone marrow transplants, immunomodulatory therapies for certain autoimmune diseases) subjects with untreated human immunodeficiency virus (hiv) infection or treated human immunodeficiency virus (hiv) infection with a cd4 count below 350 cells/mm3 in the last six months subjects actively undergoing systemic chemotherapy or radiotherapy treatment for malignancy subjects using steroids as maintenance therapy for chronic conditions subjects with active respiratory allergies or subjects expected to require anti- allergy medications during the study period for respiratory allergies. females of childbearing potential who are either pregnant or sexually active without the use of birth control. female subjects of child-bearing potential that are sexually active must have a negative baseline pregnancy test and must agree to continue an acceptable method of birth control for the duration of the study and for 1 month post-treatment. a double barrier method, oral birth control pills administered for at least 2 monthly cycles prior to study drug administration, an intrauterine device (iud), or medroxyprogesterone acetate administered intramuscularly for a minimum of one month prior to study drug administration are acceptable methods of birth control for inclusion into the study. female subjects are considered of childbearing potential unless they are postmenopausal (absence of menstrual bleeding for 1 year - or 6 months if laboratory confirmation of hormonal status), or have had a hysterectomy, bilateral tubular ligation or bilateral oophorectomy. subjects with a history of covid-19 or known to have developed anti-sars- cov-2 antibodies. subjects residing in the same household with another subject participating in the study. treatment with any investigational drug or vaccine therapy within 30 days prior to screening and willing to avoid them during the course of the study. receipt of any dose of nitazoxanide within seven days prior to screening. known sensitivity to nitazoxanide or any of the excipients comprising the study medication. subjects unable to swallow oral tablets or capsules. subjects with known severe heart, lung, neurological or other systemic disease that the investigator believes could preclude safe participation. subjects likely or expected to require hospitalization unrelated to covid-19 during the study period. subjects taking medications considered to be major cyp2c8 substrates. subjects who, in the judgment of the investigator, will be unlikely to comply with the requirements of this protocol including completion of the subject diary.

persons with any clinical sign or symptoms suggestive of severe systemic illness with covid-19, including the following: shortness of breath at rest, resting pulse ≥125 beats per minute, resting respiratory rate ≥30 breaths per minute, or spo2 ≤ 93% on room air at sea level. subjects who experienced a previous episode of acute upper respiratory tract infection, otitis, bronchitis or sinusitis or received antibiotics for these conditions within two weeks prior to and including study day 1. severely immunodeficient persons including: subjects with immunologic disorders or receiving immunosuppressive therapy (e.g., for organ or bone marrow transplants, immunomodulatory therapies for certain autoimmune diseases) subjects with untreated human immunodeficiency virus (hiv) infection or treated human immunodeficiency virus (hiv) infection with a cd4 count below 350 cells/mm3 in the last six months subjects actively undergoing systemic chemotherapy or radiotherapy treatment for malignancy subjects using steroids as maintenance therapy for chronic conditions subjects with active respiratory allergies or subjects expected to require anti- allergy medications during the study period for respiratory allergies. females of childbearing potential who are either pregnant or sexually active without the use of birth control. female subjects of child-bearing potential that are sexually active must have a negative baseline pregnancy test and must agree to continue an acceptable method of birth control for the duration of the study and for 1 month post-treatment. a double barrier method, oral birth control pills administered for at least 2 monthly cycles prior to study drug administration, an intrauterine device (iud), or medroxyprogesterone acetate administered intramuscularly for a minimum of one month prior to study drug administration are acceptable methods of birth control for inclusion into the study. female subjects are considered of childbearing potential unless they are postmenopausal (absence of menstrual bleeding for 1 year - or 6 months if laboratory confirmation of hormonal status), or have had a hysterectomy, bilateral tubular ligation or bilateral oophorectomy. subjects with a history of covid-19 or known to have developed anti-sars- cov-2 antibodies. subjects residing in the same household with another subject participating in the study. treatment with any investigational drug or vaccine therapy within 30 days prior to screening and willing to avoid them during the course of the study. receipt of any dose of nitazoxanide within seven days prior to screening. known sensitivity to nitazoxanide or any of the excipients comprising the study medication. subjects unable to swallow oral tablets or capsules. subjects with known severe heart, lung, neurological or other systemic disease that the investigator believes could preclude safe participation. subjects likely or expected to require hospitalization unrelated to covid-19 during the study period. subjects taking medications considered to be major cyp2c8 substrates. subjects who, in the judgment of the investigator, will be unlikely to comply with the requirements of this protocol including completion of the subject diary.

- persons with any clinical sign or symptoms suggestive of severe systemic illness with covid-19, including the following: 1. shortness of breath at rest, 2. resting pulse ≥125 beats per minute, 3. resting respiratory rate ≥30 breaths per minute, or 4. spo2 ≤ 93% on room air at sea level. - subjects who experienced a previous episode of acute upper respiratory tract infection, otitis, bronchitis or sinusitis or received antibiotics for these conditions within two weeks prior to and including study day 1. - severely immunodeficient persons including: 1. subjects with immunologic disorders or receiving immunosuppressive therapy (e.g., for organ or bone marrow transplants, immunomodulatory therapies for certain autoimmune diseases) 2. subjects with untreated human immunodeficiency virus (hiv) infection or treated human immunodeficiency virus (hiv) infection with a cd4 count below 350 cells/mm3 in the last six months 3. subjects actively undergoing systemic chemotherapy or radiotherapy treatment for malignancy 4. subjects using steroids as maintenance therapy for chronic conditions - subjects with active respiratory allergies or subjects expected to require anti- allergy medications during the study period for respiratory allergies. - females of childbearing potential who are either pregnant or sexually active without the use of birth control. female subjects of child-bearing potential that are sexually active must have a negative baseline pregnancy test and must agree to continue an acceptable method of birth control for the duration of the study and for 1 month post-treatment. a double barrier method, oral birth control pills administered for at least 2 monthly cycles prior to study drug administration, an intrauterine device (iud), or medroxyprogesterone acetate administered intramuscularly for a minimum of one month prior to study drug administration are acceptable methods of birth control for inclusion into the study. female subjects are considered of childbearing potential unless they are postmenopausal (absence of menstrual bleeding for 1 year - or 6 months if laboratory confirmation of hormonal status), or have had a hysterectomy, bilateral tubular ligation or bilateral oophorectomy. - subjects with a history of covid-19 or known to have developed anti-sars- cov-2 antibodies. - subjects residing in the same household with another subject participating in the study. - treatment with any investigational drug or vaccine therapy within 30 days prior to screening and willing to avoid them during the course of the study. - receipt of any dose of nitazoxanide within seven days prior to screening. - known sensitivity to nitazoxanide or any of the excipients comprising the study medication. - subjects unable to swallow oral tablets or capsules. - subjects with known severe heart, lung, neurological or other systemic disease that the investigator believes could preclude safe participation. - subjects likely or expected to require hospitalization unrelated to covid-19 during the study period. - subjects taking medications considered to be major cyp2c8 substrates. - subjects who, in the judgment of the investigator, will be unlikely to comply with the requirements of this protocol including completion of the subject diary.

- persons with any clinical sign or symptoms suggestive of severe systemic illness with covid-19, including the following: 1. shortness of breath at rest, 2. resting pulse ≥125 beats per minute, 3. resting respiratory rate ≥30 breaths per minute, or 4. spo2 ≤ 93% on room air at sea level. - subjects who experienced a previous episode of acute upper respiratory tract infection, otitis, bronchitis or sinusitis or received antibiotics for these conditions within two weeks prior to and including study day 1. - severely immunodeficient persons including: 1. subjects with immunologic disorders or receiving immunosuppressive therapy (e.g., for organ or bone marrow transplants, immunomodulatory therapies for certain autoimmune diseases) 2. subjects with untreated human immunodeficiency virus (hiv) infection or treated human immunodeficiency virus (hiv) infection with a cd4 count below 350 cells/mm3 in the last six months 3. subjects actively undergoing systemic chemotherapy or radiotherapy treatment for malignancy 4. subjects using steroids as maintenance therapy for chronic conditions - subjects with active respiratory allergies or subjects expected to require anti- allergy medications during the study period for respiratory allergies. - females of childbearing potential who are either pregnant or sexually active without the use of birth control. female subjects of child-bearing potential that are sexually active must have a negative baseline pregnancy test and must agree to continue an acceptable method of birth control for the duration of the study and for 1 month post-treatment. a double barrier method, oral birth control pills administered for at least 2 monthly cycles prior to study drug administration, an intrauterine device (iud), or medroxyprogesterone acetate administered intramuscularly for a minimum of one month prior to study drug administration are acceptable methods of birth control for inclusion into the study. female subjects are considered of childbearing potential unless they are postmenopausal (absence of menstrual bleeding for 1 year - or 6 months if laboratory confirmation of hormonal status), or have had a hysterectomy, bilateral tubular ligation or bilateral oophorectomy. - subjects with a history of covid-19 or known to have developed anti-sars- cov-2 antibodies. - subjects residing in the same household with another subject participating in the study. - treatment with any investigational drug or vaccine therapy within 30 days prior to screening and willing to avoid them during the course of the study. - receipt of any dose of nitazoxanide within seven days prior to screening. - known sensitivity to nitazoxanide or any of the excipients comprising the study medication. - subjects unable to swallow oral tablets or capsules. - subjects with known severe heart, lung, neurological or other systemic disease that the investigator believes could preclude safe participation. - subjects likely or expected to require hospitalization unrelated to covid-19 during the study period. - subjects taking medications considered to be major cyp2c8 substrates. - subjects who, in the judgment of the investigator, will be unlikely to comply with the requirements of this protocol including completion of the subject diary.