On Dec. 30, 2021, Johnson & Johnson announced preliminary results from the South African Phase 3b
Sisonke study which showed that a homologous (same vaccine) booster shot of the Johnson & Johnson COVID-19 vaccine (Ad26.COV2.S) demonstrated 85 percent effectiveness against COVID-19-related hospitalization.

The study, conducted by the South African Medical
Research Council (SAMRC), showed that the Johnson & Johnson booster reduced the risk of hospitalization from COVID-19 among healthcare workers in South Africa after Omicron became the dominant variant.