A Study to Learn About Variant-Adapted COVID-19 RNA Vaccine Candidate(s) in Healthy Children

Substudy A

Inclusion Criteria:

• Phase 1: Healthy male or female participants ≥6 months to <4 years 3 months of age,at the time of randomization.

• Phase 2/3: Healthy male or female participants ≥6 months to <5 years of age at thetime of randomization/enrollment.

Exclusion Criteria:

• Previous or current diagnosis of multisystem inflammatory syndrome in children (MIS-C).

• History of severe adverse reaction associated with a vaccine and/or severe allergicreaction (eg, anaphylaxis) to any component of the study intervention(s).

• Immunocompromised individuals with known or suspected immunodeficiency, asdetermined by history and/or laboratory/physical examination, or individuals whoreceive treatment with immunosuppressive therapy.

• Individuals with a history of autoimmune disease or an active autoimmune diseaserequiring therapeutic intervention, including but not limited to systemic lupuserythematosus. 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 (includingcytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy,within 60 days before enrollment through the conclusion of the study. Systemiccorticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalentfor persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior toenrollment through 28 days after administration of study intervention.

• Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (exceptpalivizumab), from 60 days before study intervention administration, or receipt ofany passive antibody therapy specific to COVID-19 from 90 days before studyintervention 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 ofenrollment.

Exclusion Criteria:

• Previous or current diagnosis of MIS-C.

• History of severe adverse reaction associated with a vaccine and/or severe allergicreaction (eg, anaphylaxis) to any component of the study intervention(s).

• Immunocompromised individuals with known or suspected immunodeficiency, asdetermined by history and/or laboratory/physical examination, or individuals whoreceive treatment with immunosuppressive therapy.

• Individuals with a history of autoimmune disease or an active autoimmune diseaserequiring therapeutic intervention, including but not limited to systemic lupuserythematosus.

• Prior receipt of any COVID 19 vaccine other than BNT162b2.

• Receipt of systemic treatment with known immunosuppressant medications (includingcytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy,within 60 days before enrollment through the conclusion of the study. Systemiccorticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalentfor persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior toenrollment through 28 days after administration of study intervention.

• Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (exceptpalivizumab), from 60 days before study intervention administration, or receipt ofany passive antibody therapy specific to COVID-19 from 90 days before studyintervention administration, or planned receipt throughout the study.

Substudy C

Inclusion Criteria:

• Healthy male or female participants ≥6 months to <5 years of age, at the time ofrandomization/enrollment.

Exclusion Criteria:

• Previous or current diagnosis of MIS-C.

• History of severe adverse reaction associated with a vaccine and/or severe allergicreaction (eg, anaphylaxis) to any component of the study intervention(s).

• Immunocompromised individuals with known or suspected immunodeficiency, asdetermined by history and/or laboratory/physical examination, or individuals whoreceive treatment with immunosuppressive therapy.

• Individuals with a history of autoimmune disease or an active autoimmune diseaserequiring therapeutic intervention, including but not limited to systemic lupuserythematosus.

• Prior receipt of any COVID 19 vaccine other than BNT162b2.

• Receipt of systemic treatment with known immunosuppressant medications (includingcytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy,within 60 days before enrollment through the conclusion of the study. Systemiccorticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalentfor persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior toenrollment through 28 days after administration of study intervention.

• Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (exceptpalivizumab), from 60 days before study intervention administration, or receipt ofany passive antibody therapy specific to COVID-19 from 90 days before studyintervention administration, or planned receipt throughout the study.

Substudy D

Inclusion Criteria:

• Healthy male or female participants ≥5 years to <12 years of age, at the time ofenrollment.

Exclusion Criteria:

• Previous or current diagnosis of MIS-C.

• History of severe adverse reaction associated with a vaccine and/or severe allergicreaction (eg, anaphylaxis) to any component of the study intervention(s).

• Immunocompromised individuals with known or suspected immunodeficiency, asdetermined by history and/or laboratory/physical examination, or individuals whoreceive treatment with immunosuppressive therapy.

• Individuals with a history of autoimmune disease or an active autoimmune diseaserequiring therapeutic intervention, including but not limited to systemic lupuserythematosus.

• Female who is pregnant or breastfeeding.

• Prior receipt of any COVID 19 vaccine other than BNT162b2.

• Receipt of systemic treatment with known immunosuppressant medications (includingcytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy,within 60 days before enrollment through the conclusion of the study. Systemiccorticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalentfor persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior toenrollment through 28 days after administration of study intervention.

• Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (exceptpalivizumab), from 60 days before study intervention administration, or receipt ofany passive antibody therapy specific to COVID-19 from 90 days before studyintervention administration, or planned receipt throughout the study.

Substudy E

Inclusion Criteria:

• Healthy male or female participants ≥2 years to <12 years of age, at the time ofenrollment.

Exclusion Criteria:

• Previous or current diagnosis of MIS-C.

• History of severe adverse reaction associated with a vaccine and/or severe allergicreaction (eg, anaphylaxis) to any component of the study intervention(s).

• Immunocompromised individuals with known or suspected immunodeficiency, asdetermined by history and/or laboratory/physical examination, or individuals whoreceive treatment with immunosuppressive therapy.

• Individuals with a history of autoimmune disease or an active autoimmune diseaserequiring therapeutic intervention, including but not limited to systemic lupuserythematosus.

• Any history of myocarditis or pericarditis.

• Female who is pregnant or breastfeeding.

• Previous vaccination with any COVID 19 vaccine.

• Receipt of systemic treatment with known immunosuppressant medications (includingcytotoxic agents or systemic corticosteroids, eg, for cancer) or radiotherapy,within 60 days before enrollment through the conclusion of the study. Systemiccorticosteroids (≥2 mg/kg of body weight or ≥20 mg/day of prednisone or equivalentfor persons who weigh >10 kg) for ≥14 days is prohibited from 28 days prior toenrollment through 28 days after administration of study intervention.

• Receipt of blood/plasma products, immunoglobulin, or monoclonal antibodies (exceptpalivizumab), from 60 days before study intervention administration, or receipt ofany passive antibody therapy specific to COVID-19 from 90 days before studyintervention administration, or planned receipt throughout the study.