A Study to Evaluate a Range of Dose Levels and Vaccination Intervals of Ad26.COV2.S in Healthy Adults and Adolescents

The primary purpose of this study is to assess humoral immune responses of 3 dose levels of Ad26.COV2.S administered intramuscularly (IM) as a 2-dose schedule (56 days apart); Ad26.COV2.S administered IM as a single vaccination; safety and reactogenicity of Ad26.COV2.S administered IM as a 2-dose or a single-dose schedule in adults (18-65 years or older) and to assess the safety and reactogenicity of Ad26.COV2.S, administered IM as single dose in adolescents (12-17 years) and to test both compressed and expanded 2-dose schedules of Ad26.COV2.S (28 and 84 days apart) in adults (18-55 years and 65 years or older).

The aim of the COVID-19 vaccine clinical development program is to develop a safe and effective vaccine for the prevention of COVID-19. Currently, there is only limited availability of authorized/licensed vaccines for the prevention of coronavirus disease-2019 (COVID-19). Ad26.COV2.S (also known as Ad26COVS1) is a monovalent vaccine composed of a recombinant, replication incompetent adenovirus type 26 (Ad26) vector, constructed to encode the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus spike (S) protein, which will be assessed in this study. Also, different vaccination intervals and multiple lower dose levels compared to the dose levels in the first in human study (VAC31518COV1001 \[NCT04436276\]) will be assessed. For adults, the study consists of: screening phase (28 days), vaccination phase (1-3 months) depending on the vaccination interval, and follow-up (12 months). The study duration is approximately 15 months (Groups 1-6, 8, 10 and Group 7 \[to participants for whom vaccination 2 was delayed\]), 14 months (Group 7), and 16 months (Group 9) in adult groups and approximately 13 months for adolescents group (Groups A to C). The adverse events and other safety assessments including vital signs measurements (heart rate, supine systolic and diastolic blood pressure, respiratory rate, and body temperature), and physical examinations will be assessed during the study.

Note: The Informed Consent Form dated 27-Oct-2020 is final version of the study MASTER ICF, used by local countries to prepare the local language version of the ICF, which have been approved by the Ethics Committees.

And the highlighted text in the ICF document are the guidance for country specific adaptation.

Eligibility Criteria:
Inclusion Criteria:

For Adults

* Participant must have a body mass index (BMI) less than (\<) 30.0 kilogram per meter square (kg/m\^2)
* Participant is 18 to 55 years of age, inclusive, or 65 years of age or older on the day of signing the informed consent form (ICF).
* Participant 18 to 55 years of age, inclusive: participant must be healthy, in the investigator's clinical judgment, as confirmed by medical history, physical examination, and vital signs performed at screening, and must not have comorbidities related to an increased risk of severe coronavirus disease-2019 (COVID-19), except for smoking and mild hypertension, which are allowed. Participant 65 years of age and older: In the investigator's clinical judgment, participant must be either in good or stable health. 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 COVID-19, except for smoking and mild hypertension, which are 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
* Participant will be included on the basis of physical examination, medical history, and vital signs
* All 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

For Adolescents:

* Participant is 12 to 17 years of age, inclusive, on the day of signing the informed consent form (ICF)
* Participants must have signed an ICF (or their legally acceptable representative or parent(s) \[preferably both parents if available or as per local requirements\] must sign) indicating that they understand the purpose of, and procedures required for, the study, are willing/able to adhere to the prohibitions and restrictions specified in the protocol and study procedures, and are willing (or the parents are willing for their adolescent) to participate in the study. Informed assent must be obtained from adolescents, depending on local regulations and practice
* Participant must be healthy, in the investigator's clinical judgment, as confirmed by medical history, physical examination, and vital signs performed at screening, and must not have comorbidities related to an increased risk of severe COVID-19

Exclusion Criteria:

For Adults

* 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 history of malignancy within 5 years before screening (exceptions are squamous and basal cell carcinomas of the skin and carcinoma in situ of the cervix, or malignancy, which is considered cured with minimal risk of recurrence)
* 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 treatment with immunoglobulins in the 3 months or blood products in the 4 months before the planned administration of the first dose of study vaccine or has any plans to receive such treatment during the study
* 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 Ig or monoclonal antibodies within 3 months, or received convalescent serum for COVID-19 treatment within 4 months or received an investigational vaccine (including investigational Adenoviral-vectored vaccines) 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 For Adolescents
* 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)
* Participants with a history of illness or with an ongoing illness that, in the opinion of the investigator, may pose additional risk to the participant if he/she participates in the study
* Participant has a history of Kawasaki disease
* Participant has a history of an underlying clinically significant acute or chronic medical condition or physical examination findings for which, in the opinion of the investigator, participation would not be in the best interest of the participant (example, compromise the well-being) or that could prevent, limit, or confound the protocol-specified assessments