The Phase 2 portion of the study will include approximately 200 pregnant women randomized 1:1 to receive BNT162b2 or placebo (saline) at 27 to 34 weeks' gestation. IRC review of safety data through 7 days after the second dose for all Phase 2 participants will be completed.

The Phase 3 portion of this study will assess the safety, tolerability, and immunogenicity of BNT162b2 among pregnant women enrolled at 24 to 34 weeks' gestation.

Maternal participants who originally received placebo will receive BNT162b2 at defined time points as part of the study.

Inclusion Criteria:

1. Healthy women ≥18 years of age who are between 24 0/7 and 34 0/7 weeks' gestation on the day of planned vaccination, with an uncomplicated, singleton pregnancy, who are at no known increased risk for complications.
2. Participants who are willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures.
3. Healthy participants who are determined by medical history, physical examination, and clinical judgment to be appropriate for inclusion in the study
4. Documented negative HIV antibody test (Phase 2 only), syphilis test, and HBV surface antigen test during this pregnancy and prior to randomization
5. Participant is willing to give informed consent for her infant to participate in the study
6. Capable of giving signed informed consent

Exclusion Criteria:

1. 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.
2. 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.
3. History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention or any related vaccine.
4. Participants with known or suspected immunodeficiency.
5. Bleeding diathesis or condition associated with prolonged bleeding that would in the opinion of the investigator contraindicate intramuscular injection.
6. Previous vaccination with any coronavirus vaccine.
7. Receipt of medications intended to prevent COVID 19.
8. Receipt of blood/plasma products or immunoglobulin, from 60 days before administration of study intervention, or planned receipt through delivery, with 1 exception, anti-D immunoglobulin (eg, RhoGAM), which can be given at any time.
9. Current alcohol abuse or illicit drug use.
10. Participants who receive treatment with immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids, eg, for cancer or an autoimmune disease, or planned receipt through the postvaccination blood draw.
11. Participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation.
12. Previous participation in other studies involving study intervention containing LNPs.
13. 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.
14. Participants whose unborn baby has been fathered by investigational site staff members directly involved in the conduct of the study or their family members, site staff members otherwise supervised by the investigator, or Pfizer employees directly involved in the conduct of the study.