Boston University - Clinical & Translational Science Institute

• Male or female participants between the ages of 18 and 55 years, inclusive, 65 and 85 years, inclusive, or ≥12 years, inclusive, at randomization (dependent upon study phase). For the boostability and protection-against-VOCs subset: Existing participants enrolled to receive a third dose of BNT162b2 at 30 µg or BNT162b2SA; male or female participants between the ages of 18 and 55 years, inclusive, at rerandomization. Newly enrolled participants enrolled to receive 2 doses of BNT162b2SA; male or female participants between the ages of 18 and 55 years, inclusive, at enrollment. Existing participants enrolled to receive a third dose of BNT162b2 at 5 or 10 µg; male or female participants ≥18 years at rerandomization. Note that participants <18 years of age cannot be enrolled in the EU. - Participants who are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other study procedures. - Healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. - Participants who, in the judgment of the investigator, are at risk for acquiring COVID-19. - Boostability and protection-against-VOCs existing participant subset only: Participants who provided a serum sample at Visit 3, with Visit 3 occurring within the protocol-specified window. - Capable of giving personal signed informed consent

• Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study. - Phases 1 and 2 only: Known infection with human immunodeficiency virus (HIV), hepatitis C virus (HCV), or hepatitis B virus (HBV). - History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s). - Receipt of medications intended to prevent COVID 19. - Previous clinical (based on COVID-19 symptoms/signs alone, if a SARS-CoV-2 NAAT result was not available) or microbiological (based on COVID-19 symptoms/signs and a positive SARS-CoV-2 NAAT result) diagnosis of COVID 19 - Phase 1 only: Individuals at high risk for severe COVID-19, including those with any of the following risk factors: - Hypertension - Diabetes mellitus - Chronic pulmonary disease - Asthma - Current vaping or smoking - History of chronic smoking within the prior year - BMI >30 kg/m2 - Anticipating the need for immunosuppressive treatment within the next 6 months - Phase 1 only: Individuals currently working in occupations with high risk of exposure to SARS-CoV-2 (eg, healthcare worker, emergency response personnel). - Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination. - Phase 1 only: Individuals with a history of autoimmune disease or an active autoimmune disease requiring therapeutic intervention. - Bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection. - Women who are pregnant or breastfeeding. - Previous vaccination with any coronavirus vaccine. - Individuals who receive treatment with immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids, eg, for cancer or an autoimmune disease, or planned receipt throughout the study. - Phase 1 only: Regular receipt of inhaled/nebulized corticosteroids. - Receipt of blood/plasma products or immunoglobulin, from 60 days before study intervention administration or planned receipt throughout the study. - Participation in other studies involving study intervention within 28 days prior to study entry through and including 6 months after the last dose of study intervention, with the exception of non-Pfizer interventional studies for prevention of COVID 19, which are prohibited throughout study participation. - Previous participation in other studies involving study intervention containing lipid nanoparticles. - Phase 1 only: Positive serological test for SARS-CoV-2 IgM and/or IgG antibodies at the screening visit. - Phase 1 only: Any screening hematology and/or blood chemistry laboratory value that meets the definition of a ≥ Grade 1 abnormality. - Phase 1 only: Positive test for HIV, hepatitis B surface antigen (HBsAg), hepatitis B core antibodies (HBc Abs), or hepatitis C virus antibodies (HCV Abs) at the screening visit. - Phase 1 only: SARS-CoV-2 NAAT-positive nasal swab within 24 hours before receipt of study intervention. - Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.