A Study to Evaluate Safety, Tolerability, & Immunogenicity of Multiple Formulations of BNT162b2 Against COVID-19 in Healthy Adults

Inclusion Criteria: * Male or female participants 18 - 55 years of age, inclusive, at Visit 1, (Day 1). * Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures. * Healthy participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion in the study. Note: Healthy participants with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrolment, can be included. * Capable of giving personal signed informed consent, which includes compliance with the requirements and restrictions listed in the ICD and in the protocol. * For Dose 3: Participants who received BOTH doses of the lyophilized formulation of BNT162b2 as part of the initial study. Exclusion Criteria: * 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. * Known infection with HIV, HCV, or 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). * 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. * Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination. * 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. * Receipt of medications intended to prevent COVID-19. * Individuals who receive treatment with radiotherapy or immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids (if systemic corticosteroids are administered for ≥14 days at a dose of ≥20 mg/day of prednisone or equivalent), eg, for cancer or an autoimmune disease, or planned receipt throughout the study. Inhaled/nebulized, intra-articular, intrabursal, or topical (skin or eyes) corticosteroids are permitted. * 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 and/or during study participation / Previous participation in other studies involving study intervention containing lipid nanoparticles (LNPs). * Previous participation in other studies involving study intervention containing lipid nanoparticles. * Investigator site staff or Pfizer/BioNTech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.