Phase II randomised open label trial of full and half dose J&J Ad26.CoV2.S and Pfizer BNT162b2 booster vaccinations after receiving the J&J Ad26.CoV2.S prime vaccine through the SISONKE phase IIIB implementation study.


The study aims to assess the immunogenicity and effectiveness of boosting strategies for the J&J Ad26.COV2.S vaccine. It specifically addresses several key points:

  1. Immunogenicity in Specific Populations: It focuses on populations that may have compromised immune responses, such as people living with HIV and older individuals, to understand the effectiveness of vaccination in these groups.
  2. Heterologous Prime-Boost Combinations: The study investigates heterologous prime-boost combinations, particularly using the Pfizer BNT162b2 mRNA vaccine as a booster after the J&J Ad26.COV2.S prime, to assess immune response levels.
  3. Dosage Optimization: It evaluates the potential for reducing vaccine dosage (half-dose regimens) for cost-effectiveness and to minimize adverse effects while maintaining immunogenicity.
  4. Duration of Immune Response: The study aims to determine the durability of the booster immune response over time (up to 6 months) following vaccination.


  • Dr Faeezah Patel (Principal Investigator)
  • Prof Lee Fairlie (Principal Investigator)
  • Dr Elizea Horne (Sub Investigator)
  • Dr Mrinmayee Dhar (Sub Investigator)
  • Tiffany Seef (Sub Investigator)
  • Othusitse Segalo (Sub Investigator)
  • Dr Jeanne Coetzee (Sub Investigator)

Latest Update

December 2023

For more details about the BASIS Study please email

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