Study of mRNA Vaccine Formulation Against COVID-19 in Healthy Adults 18 Years of Age and Older

The primary objectives of the study are:

* To describe the safety profile of all participants in each age group and each study intervention group up to 12 months post-last dose.
* To describe the neutralizing antibody profile at Day 1, Day 22, and Day 36 of each study intervention group.

The secondary objectives of the study are:

* To describe binding antibody profile from Day 1 to Day 387 of each study intervention group.
* To describe the neutralizing antibody profile from Day 91 to Day 387 of each study intervention group.
* To describe the occurrence of virologically-confirmed coronavirus disease-2019 (COVID-19)-like illness and serologically-confirmed SARS-CoV-2 infection.
* To evaluate the correlation/association between antibody responses to SARS-CoV-2 messenger RNA (mRNA) vaccine and the risk of virologically-confirmed COVID-19-like illness and/or serologically-confirmed severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection.

The duration of each participant's participation in the study was approximately 365 days post-last injection: approximately 386 days duration for participants receiving 2 injections and approximately 365 days duration total for participants receiving a single injection.

Eligibility Criteria:
Inclusion criteria:

* Aged \>= 18 years on the day of inclusion.
* A female participant was eligible to participate if she was not pregnant or breastfeeding and one of the following conditions applies:
* Was of non-childbearing potential. To be considered of non-childbearing potential, a female must be pre-menarche or post-menopausal for at least 1 year, or surgically sterile.

OR

* Was of childbearing potential and agreed to use an effective contraceptive method or abstinence from at least 4 weeks prior to the first vaccination until at least 12 weeks after the last vaccination.

A participant of childbearing potential must had a negative highly sensitive pregnancy test (urine or serum as required by local regulation) within 8 hours before the study intervention.

* Informed Consent Form had been signed and dated.
* Participant not eligible to receive, based on local guidance, or if eligible does not intend to receive an authorized/approved COVID-19 vaccine from first vaccination until completion of the key timepoint of Day 43 of follow-up of this study.

Exclusion criteria:

* History of COVID-19 disease or prior SARS-CoV-2 infection confirmed serologically.
* Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy, within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months).
* Chronic illness or condition considered to potentially increase the risk for severe COVID illness or that, in the opinion of the Investigator, is at a stage where it might interfere with study conduct or completion.
* Known liver disease or fatty liver.
* Positive test for chronic active Hepatitis B surface antigen, Hepatitis B core antibody, Hepatitis C antibody, or human immunodeficiency virus (HIV) antibody from blood work collected at screening visit.
* Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular vaccination based on Investigator's judgment.
* Receipt of immunoglobulins, blood or blood-derived products in the past 3 months.
* Prior administration of a coronavirus vaccine (SARS-CoV-2, SARS-CoV, Middle East Respiratory Syndrome coronavirus \[MERS-CoV\]).
* Receipt of any vaccine in the 30 days preceding the first study vaccination or planned receipt of any vaccine in the 30 days following the last study vaccination except for influenza vaccination, which might be received at least 2 weeks before and a minimum of 2 weeks after study vaccines.
* Receipt of any therapy known to have in-vitro antiviral activity against SARS-CoV-2 within 72 hours prior to the first blood draw or planned use of such therapy 72 hours prior to study immunogenicity blood draws at Day 22 and Day 36.
* Residence in a nursing home or long-term care facility.
* Health care workers providing direct patient care for COVID-19 participants.

The above information was not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.