* participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). * stage 4 severe chronic kidney disease or requiring dialysis. * screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥ 500 ms. * anticipated transfer to another hospital that is not a study center within 72 hours. * participants who are currently pregnant or who are not willing to discontinue breastfeeding. * participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. * active tuberculosis or a history of incompletely treated tuberculosis. * active, uncontrolled systemic bacterial or fungal infection(s). * apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. * apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. * apremilast only: known hypersensitivity to apremilast or any excipients in formulation. * lanadelumab only: known or suspected hypersensitivity to lanadelumab or any of its excipients. * lanadelumab only: previous (within 3 months prior to baseline) or current use of immunomodulators (eg, methotrexate, azathioprine, 6-mercaptopurine, tumor necrosis factor \[tnf\] α inhibitor, janus kinase \[jak\] inhibitor, alpha-integrin inhibitor). * lanadelumab only: known or suspected venous thromboembolism. * lanadelumab only: previous (within 3 months \[or 5 half-lives, whichever is greater\] of screening) or current use of plasma kallikrein (pkal) inhibitor or bradykinin receptor blocker. * zilucoplan only: participants with unresolved or suspected infection with neisseria meningitidis or a past history of n. meningitidis (eg, in a complement-deficient patient).

* participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). * stage 4 severe chronic kidney disease or requiring dialysis. * screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥ 500 ms. * anticipated transfer to another hospital that is not a study center within 72 hours. * participants who are currently pregnant or who are not willing to discontinue breastfeeding. * participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. * active tuberculosis or a history of incompletely treated tuberculosis. * active, uncontrolled systemic bacterial or fungal infection(s). * apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. * apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. * apremilast only: known hypersensitivity to apremilast or any excipients in formulation. * lanadelumab only: known or suspected hypersensitivity to lanadelumab or any of its excipients. * lanadelumab only: previous (within 3 months prior to baseline) or current use of immunomodulators (eg, methotrexate, azathioprine, 6-mercaptopurine, tumor necrosis factor \[tnf\] α inhibitor, janus kinase \[jak\] inhibitor, alpha-integrin inhibitor). * lanadelumab only: known or suspected venous thromboembolism. * lanadelumab only: previous (within 3 months \[or 5 half-lives, whichever is greater\] of screening) or current use of plasma kallikrein (pkal) inhibitor or bradykinin receptor blocker. * zilucoplan only: participants with unresolved or suspected infection with neisseria meningitidis or a past history of n. meningitidis (eg, in a complement-deficient patient).

participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). stage 4 severe chronic kidney disease or requiring dialysis. screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥ 500 ms. anticipated transfer to another hospital that is not a study center within 72 hours. participants who are currently pregnant or who are not willing to discontinue breastfeeding. participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. active tuberculosis or a history of incompletely treated tuberculosis. active, uncontrolled systemic bacterial or fungal infection(s). apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. apremilast only: known hypersensitivity to apremilast or any excipients in formulation. lanadelumab only: known or suspected hypersensitivity to lanadelumab or any of its excipients. lanadelumab only: previous (within 3 months prior to baseline) or current use of immunomodulators (eg, methotrexate, azathioprine, 6-mercaptopurine, tumor necrosis factor [tnf] α inhibitor, janus kinase [jak] inhibitor, alpha-integrin inhibitor). lanadelumab only: known or suspected venous thromboembolism. lanadelumab only: previous (within 3 months [or 5 half-lives, whichever is greater] of screening) or current use of plasma kallikrein (pkal) inhibitor or bradykinin receptor blocker. zilucoplan only: participants with unresolved or suspected infection with neisseria meningitidis or a past history of n. meningitidis (eg, in a complement-deficient patient).

participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). stage 4 severe chronic kidney disease or requiring dialysis. screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥ 500 ms. anticipated transfer to another hospital that is not a study center within 72 hours. participants who are currently pregnant or who are not willing to discontinue breastfeeding. participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. active tuberculosis or a history of incompletely treated tuberculosis. active, uncontrolled systemic bacterial or fungal infection(s). apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. apremilast only: known hypersensitivity to apremilast or any excipients in formulation. lanadelumab only: known or suspected hypersensitivity to lanadelumab or any of its excipients. lanadelumab only: previous (within 3 months prior to baseline) or current use of immunomodulators (eg, methotrexate, azathioprine, 6-mercaptopurine, tumor necrosis factor [tnf] α inhibitor, janus kinase [jak] inhibitor, alpha-integrin inhibitor). lanadelumab only: known or suspected venous thromboembolism. lanadelumab only: previous (within 3 months [or 5 half-lives, whichever is greater] of screening) or current use of plasma kallikrein (pkal) inhibitor or bradykinin receptor blocker. zilucoplan only: participants with unresolved or suspected infection with neisseria meningitidis or a past history of n. meningitidis (eg, in a complement-deficient patient).

- participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). - stage 4 severe chronic kidney disease or requiring dialysis. - screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥500 ms. - anticipated transfer to another hospital that is not a study center within 72 hours. - participants who are currently pregnant or who are not willing to discontinue breastfeeding. - participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. - active tuberculosis or a history of incompletely treated tuberculosis. - active, uncontrolled systemic bacterial or fungal infection(s). - apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. - apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. - apremilast only: known hypersensitivity to apremilast or any excipients in formulation. - lanadelumab only: known or suspected hypersensitivity to lanadelumab or any of its excipients. - lanadelumab only: previous (within 3 months prior to baseline) or current use of immunomodulators (eg, methotrexate, azathioprine, 6-mercaptopurine, tumor necrosis factor [tnf] α inhibitor, janus kinase [jak] inhibitor, alpha-integrin inhibitor). - lanadelumab only: known or suspected venous thromboembolism. - lanadelumab only: previous (within 3 months [or 5 half-lives, whichever is greater] of screening) or current use of plasma kallikrein (pkal) inhibitor or bradykinin receptor blocker. - zilucoplan only: participants with unresolved or suspected infection with n. meningitidis or a past history of n. meningitidis (eg, in a complement-deficient patient).

- participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). - stage 4 severe chronic kidney disease or requiring dialysis. - screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥500 ms. - anticipated transfer to another hospital that is not a study center within 72 hours. - participants who are currently pregnant or who are not willing to discontinue breastfeeding. - participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. - active tuberculosis or a history of incompletely treated tuberculosis. - active, uncontrolled systemic bacterial or fungal infection(s). - apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. - apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. - apremilast only: known hypersensitivity to apremilast or any excipients in formulation. - lanadelumab only: known or suspected hypersensitivity to lanadelumab or any of its excipients. - lanadelumab only: previous (within 3 months prior to baseline) or current use of immunomodulators (eg, methotrexate, azathioprine, 6-mercaptopurine, tumor necrosis factor [tnf] α inhibitor, janus kinase [jak] inhibitor, alpha-integrin inhibitor). - lanadelumab only: known or suspected venous thromboembolism. - lanadelumab only: previous (within 3 months [or 5 half-lives, whichever is greater] of screening) or current use of plasma kallikrein (pkal) inhibitor or bradykinin receptor blocker. - zilucoplan only: participants with unresolved or suspected infection with n. meningitidis or a past history of n. meningitidis (eg, in a complement-deficient patient).

- participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). - stage 4 severe chronic kidney disease or requiring dialysis. - screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥500 ms. - anticipated transfer to another hospital that is not a study center within 72 hours. - participants who are currently pregnant or who are not willing to discontinue breastfeeding. - participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. - apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. - apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. - apremilast only: known hypersensitivity to apremilast or any excipients in formulation.

- participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (eg, compromise their well-being) or that could prevent, limit, or confound the protocol-specified assessments (eg, participants unable to swallow study medication tablets). - stage 4 severe chronic kidney disease or requiring dialysis. - screening 12-lead electrocardiogram (ecg) with a measurable qtc interval according to fridericia correction (qtcf) ≥500 ms. - anticipated transfer to another hospital that is not a study center within 72 hours. - participants who are currently pregnant or who are not willing to discontinue breastfeeding. - participants participating in another clinical study of an investigational medicinal product or other unapproved (or investigational) treatment for covid-19. - apremilast only: current treatment with apremilast, or another agent of similar mechanism of action, for any indication within 1 week prior to first dose of investigational product. - apremilast only: concurrent use at screening or randomization of cytochrome p450 (cyp)3a inducers (eg, rifampin, phenobarbital, carbamazepine) within 1 week prior to first dose of investigational product. - apremilast only: known hypersensitivity to apremilast or any excipients in formulation.