A Study to Evaluate Dose Levels of Ad26.COV2.S Administered as a Two-dose Schedule in Healthy Adults

The purpose of this study is to demonstrate non-inferiority (NI) in terms of humoral immune responses after 6 dose levels of Ad26.COV2.S.


Eligibility Criteria:
Inclusion Criteria:

* Participant must sign an informed consent form (ICF) indicating that he or she understands the purpose, procedures and potential risks and benefits of the study, and is willing to participate in the study
* Participant must be healthy, in the investigator's clinical judgment, as confirmed by medical history, physical examination, and vital signs performed at screening. Participant may have underlying illnesses, as long as the symptoms and signs are medically controlled and not considered to be comorbidities related to an increased risk of severe Coronavirus disease 2019 (COVID-19), except for smoking, which is allowed. If on medication for a condition, the medication dose must have been stable for at least 12 weeks preceding vaccination and expected to remain stable for the duration of the study. Participant will be included on the basis of physical examination, medical history, and vital signs
* All female participants of childbearing potential must: a) have a negative highly sensitive urine pregnancy test at screening; b) have a negative highly sensitive urine pregnancy test immediately prior to each study vaccine administration
* Participant agrees to not donate bone marrow, blood, and blood products from the first study vaccine administration until 3 months after receiving the last dose of study vaccine
* Participant must be willing to provide verifiable identification, has means to be contacted and to contact the investigator during the study

Exclusion Criteria:

* Participant has a clinically significant acute illness (this does not include minor illnesses such as diarrhea or mild upper respiratory tract infection) or temperature greater than or equal to (\>=) 38.0 degree Celsius (C) (100.4 degree Fahrenheit \[F\]) within 24 hours prior to the planned first dose of study vaccine; randomization at a later date is permitted at the discretion of the investigator and after consultation with the sponsor
* Participant has a known or suspected allergy or history of anaphylaxis or other serious adverse reactions to vaccines or their excipients (including specifically the excipients of the study vaccine)
* Participant received or plans to receive: (a) licensed live attenuated vaccines - within 28 days before or after planned administration of the first or subsequent study vaccinations; and (b) other licensed (not live) vaccines - within 14 days before or after planned administration of the first or subsequent study vaccinations
* Participant received an investigational drug (including investigational drugs for prophylaxis of COVID-19) or used an invasive investigational medical device within 30 days or received investigational immunoglobulin (Ig) or monoclonal antibodies within 3 months, or received convalescent serum for COVID-19 treatment within 4 months or received an investigational vaccine within 6 months before the planned administration of the first dose of study vaccine or is currently enrolled or plans to participate in another investigational study during the course of this study
* Participant previously received a coronavirus vaccine