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 the
time 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 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.

Exclusion Criteria:

- Previous or current diagnosis of 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.

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

- 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 C

Inclusion Criteria:

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

Exclusion Criteria:

- Previous or current diagnosis of 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.

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

- 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 D

Inclusion Criteria:

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

Exclusion Criteria:

- Previous or current diagnosis of 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.

- Female who is pregnant or breastfeeding.

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

- 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 E

Inclusion Criteria:

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

Exclusion Criteria:

- Previous or current diagnosis of 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.

- 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 (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.