{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,17]],"date-time":"2026-03-17T06:33:46Z","timestamp":1773729226751,"version":"3.50.1"},"reference-count":0,"publisher":"South African Medical Association NPC","issue":"7","license":[{"start":{"date-parts":[[2025,8,1]],"date-time":"2025-08-01T00:00:00Z","timestamp":1754006400000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["S Afr Med J"],"abstract":"<jats:p>\n\n\n\nBackground. From March 2020 to June 2022, South Africa (SA) confronted successive waves of COVID\u201019, each linked to emerging SARS\u2010CoV\u20102 variants. Vaccines played a critical role in preventing severe disease and death, but as new SARS\u2010CoV\u20102 variants emerged, with increasing breakthrough infections, questions arose about the real\u2010world effectiveness of first\u2010generation vaccines containing the ancestral strain against evolving variants including Delta and Omicron BA.1 and BA.4\/5 SARS\u2010CoV\u20102.\nObjectives. To assess the real\u2010world effectiveness of ancestral strain booster doses (either Ad26.COV2.S or BNT162b2) in preventing severe COVID\u201019 outcomes, including hospitalisation, admission to critical care and death, among essential workers in SA who received a primary dose of Ad26.COV2.S against emerging SARS\u2010CoV\u20102 variants.\nMethods. A retrospective cohort study was conducted using data from a large private health insurance scheme. Individuals who received a single dose of Ad26.COV2.S as their primary vaccination were included. Time\u2010varying Cox regression models were used to assess the effectiveness of boosting with either Ad26.COV2.S or BNT162b2 v. not boosting against severe COVID\u201019 outcomes associated with emerging variants, adjusting for various demographic and clinical factors.\nResults. By August 2021, a total of 407 961 individuals received a first dose of Ad26.COV2.S, of whom 350 688 were eligible for and 332 286 included in the vaccine effectiveness (VE) analysis. Of these, 206 359 (62%) received no further doses, while 113 957 (34%) received a second dose of Ad26.COV2.S and 11 970 (4%) received a second dose of BNT162b2 by August 2022. During the follow\u2010up period (November 2021 \u2010 August 2022), 1 125 COVID\u201019\u2010related hospital admissions, 198 admissions to critical care and 41 COVID\u201019\u2010related deaths were recorded. Adjusted relative VE against severe outcomes was 34% (95% confidence interval (CI) 19 \u2010 45) for hospital admission, 51% (95% CI 22 \u2010 70) for critical care admission, and 89% (95% CI 13 \u2010 98) for COVID\u201019\u2010 related death.\nConclusion. While most participants remained unboosted, administration of either ancestral strain Ad26.COV2.S or BNT162b2 vaccination provided protection against severe COVID\u201019 outcomes among essential workers in SA during the dominance of the Omicron BA.1 and BA.4\/5 variants, demonstrating cross\u2010strain protection.\n\n\n\n<\/jats:p>","DOI":"10.7196\/samj.2025.v115i7.2532","type":"journal-article","created":{"date-parts":[[2025,8,8]],"date-time":"2025-08-08T07:22:22Z","timestamp":1754637742000},"page":"e2532","source":"Crossref","is-referenced-by-count":1,"title":["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"],"prefix":"10.7196","volume":"115","author":[{"given":"L","family":"Fairall","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"N","family":"Yende-Zuma","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tarylee","family":"Reddy","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"N","family":"Garrett","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"A","family":"Goga","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"S","family":"Bennet","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"N","family":"Folb","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"I","family":"Seocharan","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"S","family":"Mametja","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"M","family":"Semenya","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"S R N","family":"Simelane","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"family":"L-G","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"G E","family":"Gray","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"4425","published-online":{"date-parts":[[2025,8,1]]},"container-title":["South African Medical Journal"],"original-title":[],"link":[{"URL":"https:\/\/samajournals.co.za\/index.php\/samj\/article\/download\/2532\/1468","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/samajournals.co.za\/index.php\/samj\/article\/download\/2532\/1468","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,8,8]],"date-time":"2025-08-08T07:22:22Z","timestamp":1754637742000},"score":1,"resource":{"primary":{"URL":"https:\/\/samajournals.co.za\/index.php\/samj\/article\/view\/2532"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,8,1]]},"references-count":0,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2025,8,1]]}},"URL":"https:\/\/doi.org\/10.7196\/samj.2025.v115i7.2532","relation":{},"ISSN":["2078-5135","0256-9574"],"issn-type":[{"value":"2078-5135","type":"electronic"},{"value":"0256-9574","type":"print"}],"subject":[],"published":{"date-parts":[[2025,8,1]]}}}