a study of ad26.cov2.s administered as booster vaccination in adults who have previously received primary vaccination with ad26.cov2.s or bnt162b2

Conditions: Coronavirus Disease

Summary: the purposes of this study are to demonstrate the non-inferiority (ni) of the neutralizing antibody response to the original strain 14 days after booster vaccination with ad26.cov2.s at the different dose levels, administered greater than or equal to (\>=) 6 months after single-dose primary vaccination with ad26.cov2.s, compared to the neutralizing antibody response to the original strain induced by single-dose primary vaccination with ad26.cov2.s; to demonstrate the ni of the neutralizing antibody response to the leading variant of high consequence or concern 14 days after booster vaccination with ad26.cov2.s at the 5\*10\^10 virus particle (vp) dose level, administered \>= 6 months after single-dose primary vaccination with ad26.cov2.s (5\*10\^10 vp dose level), compared to the neutralizing antibody response to the leading variant of high consequence or concern induced by single-dose primary vaccination with ad26.cov2.s at the 5\*10\^10 vp dose level, if feasible; to demonstrate the ni of the neutralizing antibody response to the original strain 14 days after booster vaccination with ad26.cov2.s at the different dose levels administered \>=6 months after completing a 2-dose primary vaccination with pfizer bnt162b2, compared to the neutralizing antibody response to the original strain induced by 2-dose primary vaccination with pfizer bnt162b2; to demonstrate the ni of neutralizing antibody response to the leading variant of high consequence or concern 14 days after booster vaccination with ad26.cov2.s at the 5\*10\^10 vp dose level, administered \>= 6 months after completing a 2-dose primary vaccination with pfizer bnt162b2, compared to the neutralizing antibody response to the leading variant of high consequence or concern induced by 2-dose primary vaccination with pfizer bnt162b2, if feasible.


Eligibility criteria:
inclusion criteria: * cohort 1: participant received ad26.cov2.s in vac31518cov3001. the interval between the ad26.cov2.s primary vaccination should preferably be greater than or equal to (\>=) 6 months prior to study vaccination on vac31518cov2008, however a window of maximum -20 days is allowed; cohort 2: participant completed primary vaccination with a 2-dose regimen of bnt162b2 vaccine. the last dose of btn162b2 should preferably be \>=6 months prior to study vaccination on cov2008, however a window of a maximum of -20 days is allowed * participant must provide consent 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 agrees to not donate bone marrow, blood, and blood products from the study vaccine administration until 3 months after receiving the study vaccine * participant must be willing to provide verifiable identification, has means to be contacted and to contact the investigator during the study * participant must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) (that is, the coronavirus disease (covid-19) signs and symptoms surveillance question, the e-diary, and the electronic patient-reported outcomes (epros). participants with visual impairment are eligible for study participation and may have caregiver assistance in completing the ecoa questionnaires 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 \>= 38.0 degree celsius (c) (100.4 degree fahrenheit \[f\]) within 24 hours prior to the planned study vaccination; randomization at a later date is permitted at the discretion of the investigator. please notify the sponsor (or medical monitor) of this decision * 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 (ig) in the 3 months or exogenous blood products (autologous blood transfusions are not exclusionary) in the 4 months before the planned administration of the study vaccine or has any plans to receive such treatment during the study * participant has a known history of confirmed severe acute respiratory syndrome coronavirus-2 (sars-cov-2) infection * participant has a history of heparin-induced thrombocytopenia or thrombosis in combination with thrombocytopenia * participant has a history of acute polyneuropathy (example. guillain-barre syndrome) * history of capillary leak syndrome