Inclusion Criteria:  Male or female <18 years of age. Participants will be stratified into different age cohorts (≥12 to < 18 years, ≥5 to < 12 years, ≥2 to < 5 years, and < 2 years of age) based on the age on the day of inclusion. Individuals and their legally authorized representative (LAR) are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests and other study procedures. Individuals are willing and able to give an assent (if applicable) and their LARs are willing and able to give informed consent on their behalf, prior to screening Healthy participants (phase 2 and phase 3) or participants with pre-existing medical conditions who are in a stable medical condition (phase 2) For infants (<1-year-old) - born at full term (gestational age ≥37 weeks) and with a normal birth weight (≥2500 grams). Female participants of childbearing potential may be enrolled in the study, if the participant has practiced highly effective contraception for 30 days prior to vaccination, and has a negative pregnancy test on the day of vaccination and has agreed to continue adequate contraception for 3 months after the last vaccination  Exclusion Criteria:  Individuals with fever >38.0°C [≥ 100.4°F] (irrespective of method used), or any acute illness at baseline (Day 1) or within 3 days prior to randomization. Individuals with laboratory-confirmed SARS-CoV-2 infection [as defined by Rapid COVID Antigen Test or an equivalent at Day 1] or with history of laboratory-confirmed/medically-diagnosed COVID-19 (for phase 2 participants only). Individuals who have received an investigational or licensed COVID-19 vaccine prior to Day 1, or plan to receive an investigational or licensed COVID-19 vaccine during the study period. Any confirmed or suspected immunosuppressive or immunodeficient condition resulting from disease [e.g., malignancy, human immunodeficiency virus (HIV) infection] or immunosuppressive/cytotoxic therapy (e.g., systemic corticosteroids, medications used for cancer chemotherapy, organ transplantation or to treat autoimmune disorders) within 3 months prior to Day 1. Inhaled, intranasal, topical steroids as well as a single dose of systemic steroids, are allowed. Individuals with any progressive or severe neurologic disorder, seizure disorder (including febrile seizures) or history of Guillain-Barré syndrome. Individuals who are pregnant, or breastfeeding, or planning to become pregnant while enrolled in this study or during the study period. Individuals who have a history of severe adverse reaction associated with a vaccine or severe allergic reaction Individuals who have received any other investigational product within 30 days prior to Day 1 or intend to participate in another clinical study at any time during the conduct of this study. Individuals who have received any other licensed vaccines within 14 days prior to enrollment in this study or who are planning to receive any vaccine up to 28 days after the second (phase 2) or third (phase 3) vaccination. Individuals with known bleeding disorder that would, in the opinion of the investigator, contraindicate intramuscular injection Administration of intravenous immunoglobulins and/or any blood products within 3 months prior to enrollment or planned administration during the study period Individuals with any condition that, in the opinion of the investigator, would interfere with the primary study objectives or pose additional risk to the participant