Sisonke 2 - A COVID-19 Vaccine Boost Open Label Study. (Sisonke Boost)

August 27, 2026 updated by: Wits Health Consortium (Pty) Ltd

Open-label, Single-arm Phase 3B Implementation Study to Evaluate the Effectiveness of the Homologous Boost of Ad26.COV2.S COVID-19 Vaccine Following the Prime Dose Among Sisonke Participants in South Africa(VAC31518COV30XX)

To evaluate the effectiveness of the single dose Ad26.COV2.S COVID-19 vaccine plus a homologous boostwith Ad26.COV2.S COVID-19 vaccine among Sisonke participants as compared to unboosted Sisonkeparticipants; vaccinated; and unvaccinated populations in South Africa

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

Purpose To evaluate the effectiveness and safety of the single dose Ad26.COV2.S (Jansen) COVID-19 vaccine plus a homologous boost with Ad26.COV2.S (Janssen) COVID-19 vaccine among Sisonke participants as compared to unboosted Sisonke participants

In addition the investigators will continue to evaluate VE of the Sisonke Boost compared to:

i) Vaccinated populations pre boosts ii) Unvaccinated populations in South Africa.

Study design Open-label, single-arm phase 3B vaccine implementation study

Rationale South Africa is severely affected by the global COVID-19 epidemic, and following the initial prime vaccination among HCWs in the first 4 months of 2021. New data has demonstrated the safety and effectiveness of a booster dose given two months or more after the initial Ad26.COV2.S. This provides the rationale and feasibility for the evaluation of a homologous booster vaccine dose to the cohort of vaccinated Sisonke participants to inform the larger vaccine rollout.

Study participants Sisonke participants age 18 and over working in the South African public and private health care sector (approx N=500 000) who were enrolled in Sisonke and have not subsequently had a further booster vaccine dose.

Study sites Department of Health Vaccine Administration Sites across South Africa supported by the Sisonke (Together) (VAC31518COV3012) Trial Research Site Investigators and Study Staff

Study duration Participants will receive a homologous Ad26.COV2.S (Janssen) booster dose of vaccine at least 6 months post the prime vaccination. The investigators will monitor outcomes utilising the DATCOV surveillance system and NHLS/NICD SARS COV-2 testing databases for up to 2 years post initial vaccination.

Study products Ad26.COV2.S by Janssen administered as a single dose followed by a single booster injection.

Primary objectives • To assess the effectiveness of Ad26.COV2.S vaccine as a homologous boost on severe COVID, hospitalizations and deaths in Sisonke participants as compared with the unboosted Sisonke populations.

Secondary objectives To assess the effectiveness of Ad26.COV2.S vaccine as a homologous boost on severe COVID, hospitalizations and deaths in Sisonke participants as compared vaccinated and unvaccinated populations of essential workers in South Africa.

  • To estimate the incidence of symptomatic SARS CoV-2 infections in Sisonke participants following a boost compared with the unboosted Sisonke populations and general vaccinated and unvaccinated population in South Africa
  • To estimate booster dose uptake among Sisonke participants in South Africa
  • To monitor the genetic diversity of breakthrough SARS CoV-2 infections.
  • To monitor safety in the case of homologous boosts in Sisonke participants.

Study Type

Interventional

Enrollment (Actual)

500000

Phase

  • Phase 3

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • South Africa
      • Cape Town, South Africa, 7975
        • Desmond Tutu Health Foundation - Masiphumelele Research Office
      • Rustenburg, South Africa, 0299
        • The Aurum Institute: Rustenburg Clinical Research Centre, Dr Lawrence
    • Eastern Cape
      • Mthatha, Eastern Cape, South Africa, 5100
        • Nelson Mandela Academic Clinical Research Unit (NeMACRU)
      • Port Elizabeth, Eastern Cape, South Africa, 6001
        • PHOENIX Pharma Pty Ltd
    • Free State
      • Bloemfontein, Free State, South Africa, 9300
        • Josha Research
    • Gauteng
      • Johannesburg, Gauteng, South Africa, 1862
        • Perinatal HIV Research Unit (PHRU), SOWETO
      • Johannesburg, Gauteng, South Africa, 2000
        • Clinical HIV Research Unit (CHRU),
      • Pretoria, Gauteng, South Africa, 0152
        • Setshaba Research Centre,
      • Pretoria, Gauteng, South Africa
        • Ndlovu Research Centre
      • Pretoria, Gauteng, South Africa, 0000
        • MeCRU Clinical Research Unit
      • Pretoria, Gauteng, South Africa, 2059
        • The Aurum Institute Clinical Research Centre, Pretoria
    • Gauteng - South
      • Johannesburg, Gauteng - South, South Africa, 1632
        • The Aurum Institute: Tembisa Clinical Research Centre
      • Johannesburg, Gauteng - South, South Africa, 1809
        • Perinatal HIV Research Unit Kliptown
    • KwaZulu-Natal
      • Bothas Hill, KwaZulu-Natal, South Africa, 3660
        • Botha's Hill Clinical Research Site
      • Durban, KwaZulu-Natal, South Africa, 4001
        • CAPRISA eThekwini Clinical Research Site, Dr
      • Durban, KwaZulu-Natal, South Africa, 4030
        • Chatsworth Clinical Research Site
      • Durban, KwaZulu-Natal, South Africa
        • CAPRISA Vulindlela Clinical Research Site, Dr Disebo Makhaza
      • Ladysmith, KwaZulu-Natal, South Africa, 3370
        • Qhakaza Mbokodo Research Clinic
      • Tongaat, KwaZulu-Natal, South Africa, 4400
        • Tongaat Clinical Research Site, Dr
    • Mpumalanga
      • Middleburg, Mpumalanga, South Africa, 1050
        • Mzansi Ethical Research Centre
    • North West
      • Klerksdorp, North West, South Africa, 2571
        • The Aurum Institute Klerksdorp Clinical Research Centre
    • Western Cape
      • Cape Town, Western Cape, South Africa, 7505
        • FAMCRU (Family Clinical Research Unit),
      • Cape Town, Western Cape, South Africa, 7530
        • TASK Central
      • Cape Town, Western Cape, South Africa, 7530
        • TASK Clinical Research Centre
      • Cape Town, Western Cape, South Africa, 7925
        • Desmond Tutu Health Foundation CTU J52 Old Main Building Groote SchuurHospital
      • Cape Town, Western Cape, South Africa, 7100
        • TASK Applied Science, Delft Day Hospital Premises
      • Cape Town, Western Cape, South Africa, 7100
        • TASK Applied Science, Dr Ivans Toms Clinic Premises
      • Cape Town, Western Cape, South Africa, 7530
        • TASK Applied Science, Brooklyn Chest Hospital Premises
      • Cape Town, Western Cape, South Africa, 7781
        • Emavundleni Research Centre
      • George, Western Cape, South Africa, 6529
        • TASK Eden
      • Worcester, Western Cape, South Africa, 6850
        • South African Vaccine Initiative (SATVI)

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria

  • Age 18 and older
  • All Sisonke participants
  • Received a priming Ad26.SARS.COV.2.S vaccination as part of the Sisonke study at least 6 months prior
  • Participants who are pregnant or report breastfeeding at the time of enrolment may be included.
  • Willingness and ability to comply with vaccination plan and other study procedures.
  • Capable of giving electronic or personal signed informed consent as described in Appendix 5, which includes compliance with the requirements in this protocol.

Exclusion Criteria:

  • Participants who have received boosting vaccination through other means.
  • Any significant acute or chronic medical condition, situation or circumstance that in the opinion of the PI/designee makes the participant unsuitable for participation in the study, or jeopardises the safety or rights of the participant
  • Current participation in any other research studies that would interfere with the objectives of this study. The determination of whether participation in another study would be exclusionary for a given participant will be made by the PI/designee.
  • Participants with a history of heparin-induced thrombocytopenia or TTS

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Non-Randomized
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: Sisonke Heterologous mRNA-1273 boost after prime with Ad26.COV2.S
Biological: Sisonke Heterologous mRNA-1273 boost after prime with Ad26.COV2.S

To evaluate the effectiveness and safety of the single dose Ad26.COV2.S (Jansen) COVID-19 vaccine plus a homologous boost with Ad26.COV2.S (Janssen) COVID-19 vaccine among Sisonke participants as compared to unboosted Sisonke participants

In addition we will continue to evaluate VE of the Sisonke Boost compared to:

i) Vaccinated populations pre boosts ii) Unvaccinated populations in South Africa.

Other Names:
  • Booster vaccine
Drug: Sisonke Heterologous mRNA-1273 boost after prime with Ad26.COV2.S
Sisonke Heterologous mRNA-1273 boost after prime with Ad26.COV2.S

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
To assess the effectiveness of Ad26.COV2.S (Janssen) boost vaccine on severe COVID, hospitalizations and deaths in Sisonke participants as compared to unboosted Sisonke participants (single Ad26 vaccine only)
Time Frame: 24 Months
Rates of hospitalizations and deaths among boosted Sisonke participants versus unboosted Sisonke participants and unvaccinated populations in South Africa
24 Months

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
To assess the effectiveness of Ad26.COV2.S (Janssen) boost vaccine on severe COVID, hospitalizations and deaths in Sisonke participants as compared to the vaccinated and unvaccinated populations (no vaccination) in South Africa.
Time Frame: 24 Months
Rates of hospitalizations and deaths among boosted Sisonke participants versus unboosted vaccinated and unvaccinated populations in South Africa
24 Months
To estimate the incidence of symptomatic SARS CoV-2 infections among boosted Sisonke ppts.
Time Frame: 24 months

Incidence rate of SARS CoV-2 infection as indicated by self-report and validation in national laboratory records.

Rates of severe disease in Sisonke participants who are found to be RT-PCR positive at any time up to 2 years post prime vaccination
24 months
To monitor the genetic diversity of breakthrough SARS CoV-2 infections
Time Frame: 24 Months
Genetic diversity of breakthrough infection virus as determined by whole genome sequencing. This will be recovered from national laboratories.
24 Months
To estimate booster vaccine uptake among Sisonke participants in South Africa
Time Frame: 24 Months
Proportion of Sisonke participants approached for study participation taking part in the boost study and receiving the booster vaccine
24 Months
To monitor safety in homologous boosts
Time Frame: 24 Months
All SAEs and events of special interest will be collected and reported.
24 Months

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Wits Health Consortium (Pty) Ltd

Collaborators

Fred Hutchinson Cancer Center
Janssen Vaccines & Prevention B.V.
Right to Care
National Department of Health of South Africa
KwaZulu-Natal Research Innovation and Sequencing Platform - KRISP
Hutchinson Center Research Institute of South Africa (HCRISA)
Bio Analytical Research Corporation
Dis-Chem Pharmacy
BioVac
Biocair
Clinical Laboratory Services
National Institute of Communicable Diseases - NICD
Institute of Infectious Disease and Molecular Medicine

Investigators

  • Principal Investigator: Glenda Gray, MBChB, Non-Executive Director

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

November 10, 2021

Primary Completion (Actual)

January 31, 2022

Study Completion (Actual)

June 30, 2023

Study Registration Dates

First Submitted

November 9, 2021

First Submitted That Met QC Criteria

December 4, 2021

First Posted (Actual)

December 8, 2021

Study Record Updates

Last Update Posted (Actual)

September 1, 2026

Last Update Submitted That Met QC Criteria

August 27, 2026

Last Verified

August 1, 2026

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

  • Sisonke Boost Open Label Study

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

All study team scientists will disseminate the trial results as broadly as possible. Data will be shared with JNJ prior to release to the public. The study data will be published consistent with normal scientific practices.

The results from this research may also be disseminated through presentations at scientific institutions/ meetings, and/or publication in scientific journals. All publications will be uploaded to a publication repository. After sharing the results with study participants, they will be presented to communities from which participants are recruited, following Good Participatory Practice guidelines. The results will also be shared with global and local policy makers. Summary results of the trial will be made publicly available through the clinical trial registry. Any datasets used for analysis in publications can be requested by investigators via an online request to the organisation. Measures will be taken to protect identifiable information in the datasets

IPD Sharing Time Frame

Within 12 months of completion of study

IPD Sharing Access Criteria

on request

IPD Sharing Supporting Information Type

  • CSR

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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