Fairall, L.; Yende-Zuma, N.; Reddy, T. .; Garrett, N.; Goga, A.; Bennet, S.; Folb, N.; Seocharan, I.; Mametja, S.; Semenya, M.; Simelane, S. R. N.; L-G; Gray, G. E. Real-World Effectiveness of Ad26.COV2.S or BNT162b2 Booster Vaccines Against Severe COVID-19 in Adults Who Received a Primary Dose of Ad26.COV2.S in South Africa During the Delta Period: A Retrospective Cohort Study Using Medical Scheme Data. S Afr Med J 2025, 115 (7), e2532 . https://doi.org/10.7196/SAMJ.2025.v115i7.2532.