Open-label, phase 3 study to evaluate the effectiveness of heterologous mRNA-1273 boosting of the single or two dose Ad26.COV2.S COVID-19 vaccine among health care workers in South Africa.


South Africa is severely affected by the global COVID-19 pandemic. As part of the Sisonke study, HCWs received a single dose of Ad26.COV2.S vaccine between 17 February and 17 May 2021, and were then offered a second dose between 8 November and 17 December 2021. Immunogenicity studies have since indicated that a heterologous mRNA vaccine boost strategy may elicit stronger neutralizing antibody responses among people who received the Ad26.COV2.S and other vector-based vaccines.


  • Dr Faeezah Patel , Principal Investigator
  • Prof Lee Fairlie
  • Dr Elizea Horne
  • Dr Robert Kieser
  • Tiffany Seef
  • Othusiste Segalo
  • Dr Mrinmayee Dhar

Latest Update

May 2023

For more about SHERPA/SISONKE 4 study please email

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