* previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). * history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). * immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. * individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. note: stable type 1 diabetes and hypothyroidism are permitted. * any history of myocarditis or pericarditis. * previous vaccination with any covid-19 vaccine. * receipt of systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy, within 60 days before enrollment through the conclusion of the study. systemic corticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalent for persons who weigh \>10 kg) for ≥14 days is prohibited from 28 days prior to enrollment through 28 days after administration of study intervention. * receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to \<5 years of age, at the time of enrollment.

* previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). * history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). * immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. * individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. note: stable type 1 diabetes and hypothyroidism are permitted. * any history of myocarditis or pericarditis. * previous vaccination with any covid-19 vaccine. * receipt of systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy, within 60 days before enrollment through the conclusion of the study. systemic corticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalent for persons who weigh \>10 kg) for ≥14 days is prohibited from 28 days prior to enrollment through 28 days after administration of study intervention. * receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to \<5 years of age, at the time of enrollment.

previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. note: stable type 1 diabetes and hypothyroidism are permitted. any history of myocarditis or pericarditis. previous vaccination with any covid-19 vaccine. receipt of systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy, within 60 days before enrollment through the conclusion of the study. systemic corticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalent for persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior to enrollment through 28 days after administration of study intervention. receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to <5 years of age, at the time of enrollment.

previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. note: stable type 1 diabetes and hypothyroidism are permitted. any history of myocarditis or pericarditis. previous vaccination with any covid-19 vaccine. receipt of systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy, within 60 days before enrollment through the conclusion of the study. systemic corticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalent for persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior to enrollment through 28 days after administration of study intervention. receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to <5 years of age, at the time of enrollment.

previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. note: stable type 1 diabetes and hypothyroidism are permitted. previous vaccination with any covid-19 vaccine. receipt of systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy, within 60 days before enrollment through the conclusion of the study. systemic corticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalent for persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior to enrollment through 28 days after administration of study intervention. receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to <5 years of age, at the time of enrollment.

previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention, including but not limited to systemic lupus erythematosus. note: stable type 1 diabetes and hypothyroidism are permitted. previous vaccination with any covid-19 vaccine. receipt of systemic treatment with known immunosuppressant medications (including cytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy, within 60 days before enrollment through the conclusion of the study. systemic corticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalent for persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior to enrollment through 28 days after administration of study intervention. receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to <5 years of age, at the time of enrollment.

previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention. previous vaccination with any coronavirus vaccine. receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to <5 years of age, at the time of enrollment.

previous or current diagnosis of multisystem inflammatory syndrome in children (mis-c). history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination, or individuals who receive treatment with immunosuppressive therapy. individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention. previous vaccination with any coronavirus vaccine. receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (except palivizumab), from 60 days before study intervention administration, or receipt of any passive antibody therapy specific to covid-19 from 90 days before study intervention administration, or planned receipt throughout the study. substudy b inclusion criteria: - healthy male or female participants = ≥6 months to <5 years of age, at the time of enrollment.