{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,15]],"date-time":"2026-04-15T18:02:27Z","timestamp":1776276147242,"version":"3.50.1"},"reference-count":41,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2025,7,9]],"date-time":"2025-07-09T00:00:00Z","timestamp":1752019200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Department de Salut from Generalitat de Catalunya","award":["SLT017\/20\/000055"],"award-info":[{"award-number":["SLT017\/20\/000055"]}]},{"name":"Department de Salut from Generalitat de Catalunya","award":["SLT021_000038"],"award-info":[{"award-number":["SLT021_000038"]}]},{"name":"Department de Salut from Generalitat de Catalunya","award":["INT23\/00040"],"award-info":[{"award-number":["INT23\/00040"]}]},{"name":"Spanish Ministry of Science and Innovation","award":["SLT017\/20\/000055"],"award-info":[{"award-number":["SLT017\/20\/000055"]}]},{"name":"Spanish Ministry of Science and Innovation","award":["SLT021_000038"],"award-info":[{"award-number":["SLT021_000038"]}]},{"name":"Spanish Ministry of Science and Innovation","award":["INT23\/00040"],"award-info":[{"award-number":["INT23\/00040"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vaccines"],"abstract":"<jats:p>Background: SARS-CoV-2 booster vaccination remains essential to prevent severe COVID-19, particularly in vulnerable populations such as older adults. This study evaluated the durability and dynamics of immune responses following booster vaccination(s) in &gt;65-year-old individuals and examined their association with protection against new infections. Methods: Immune responses were evaluated at 3, 9, and 15 months post-booster, measuring SARS-CoV-2-specific IgG antibodies against spike [IgG(S)] and nucleocapsid [IgG(N)] proteins, neutralizing activity against the Omicron BA.2 variant, and cellular immunity. A subset of participants was tested before booster administration. Regression analyses examined the influence of clinical and immunological factors\u2014including a bivalent fourth dose\u2014on infection risk over time. Results: Booster vaccination significantly enhanced IgG(S) and neutralizing capacity, peaking at 3 months. Although a decline was observed by 9 months, responses remained above baseline. Individuals with prior SARS-CoV-2 infection exhibited higher IgG(S) levels and neutralizing titers, and significantly lower reinfection rates (15%), compared to uninfected individuals. A fourth vaccine dose further increased IgG(S) levels. While neutralizing capacity was not consistently enhanced by the fourth dose, recipients experienced a lower rate of new infections. Immune trajectory analyses revealed that breakthrough infections elicited strong humoral responses comparable to those seen in previously infected individuals, highlighting the role of hybrid immunity. Conclusions: In older adults, booster vaccination induces durable immune responses, with hybrid immunity offering enhanced protection. A fourth dose boosts antibody levels and reduces infection risk, supporting its use in this high-risk group. Continued monitoring is needed to determine the long-term effectiveness of boosters, particularly against emerging variants.<\/jats:p>","DOI":"10.3390\/vaccines13070738","type":"journal-article","created":{"date-parts":[[2025,7,11]],"date-time":"2025-07-11T13:44:19Z","timestamp":1752241459000},"page":"738","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Immune Durability and Breakthrough Infections 15 Months After SARS-CoV-2 Boosters in People over 65: The IMMERSION Study"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3309-5360","authenticated-orcid":false,"given":"Concepci\u00f3","family":"Viol\u00e1n","sequence":"first","affiliation":[{"name":"Unitat de Suport a la Recerca Metropolitana Nord, Institut Universitari d\u2019Investigaci\u00f3 en Atenci\u00f3 Prim\u00e0ria Jordi Gol (IDIAP Jordi Gol), Mare de D\u00e9u de Guadalupe 2, Planta 1\u00aa, Matar\u00f3, 08303 Barcelona, Spain"},{"name":"Germans Trias i Pujol Research Institute (IGTP), 08916 Badalona, Spain"},{"name":"Grup de Recerca en Impacte de les Malalties Cr\u00f2niques i les seves Traject\u00f2ries (2021-SGR-01537), IDIAPJGol, 08007 Barcelona, Spain"},{"name":"Red de Investigaci\u00f3n en Cronicidad, Atenci\u00f3n Primaria y Prevenci\u00f3n y Promoci\u00f3n de la Salud (RICCAPPS), Instituto de Salud Carlos III, 08196 Madrid, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Bibiana","family":"Quirant-S\u00e1nchez","sequence":"additional","affiliation":[{"name":"Germans Trias i Pujol Research Institute (IGTP), 08916 Badalona, Spain"},{"name":"Immunology Department, Federation of Clinical Immunology Societies Center of Excellence, Universitat Aut\u00f2noma de Barcelona, 08913 Cerdanyola del Vall\u00e8s, Spain"},{"name":"Laboratori Clinic Metropolitana Nord, Immunology Division, Hospital Universitari Germans Trias i Pujol, 08916 Badalona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-4552-6268","authenticated-orcid":false,"given":"Maria","family":"Palau-Antoja","sequence":"additional","affiliation":[{"name":"Unitat de Suport a la Recerca Metropolitana Nord, Institut Universitari d\u2019Investigaci\u00f3 en Atenci\u00f3 Prim\u00e0ria Jordi Gol (IDIAP Jordi Gol), Mare de D\u00e9u de Guadalupe 2, Planta 1\u00aa, Matar\u00f3, 08303 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dolors","family":"Palacin","sequence":"additional","affiliation":[{"name":"Unitat de Suport a la Recerca Metropolitana Nord, Institut Universitari d\u2019Investigaci\u00f3 en Atenci\u00f3 Prim\u00e0ria Jordi Gol (IDIAP Jordi Gol), Mare de D\u00e9u de Guadalupe 2, Planta 1\u00aa, Matar\u00f3, 08303 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5162-8920","authenticated-orcid":false,"given":"Edwards","family":"Pradenas","sequence":"additional","affiliation":[{"name":"IrsiCaixa, Carretera de Canyet, s\/n, 08916 Badalona,   Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Macedonia","family":"Trigueros","sequence":"additional","affiliation":[{"name":"IrsiCaixa, Carretera de Canyet, s\/n, 08916 Badalona,   Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3188-7268","authenticated-orcid":false,"given":"Guillem","family":"Pera","sequence":"additional","affiliation":[{"name":"Unitat de Suport a la Recerca Metropolitana Nord, Institut Universitari d\u2019Investigaci\u00f3 en Atenci\u00f3 Prim\u00e0ria Jordi Gol (IDIAP Jordi Gol), Mare de D\u00e9u de Guadalupe 2, Planta 1\u00aa, Matar\u00f3, 08303 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0927-1945","authenticated-orcid":false,"given":"Gemma","family":"Molist","sequence":"additional","affiliation":[{"name":"Unitat de Suport a la Recerca Metropolitana Nord, Institut Universitari d\u2019Investigaci\u00f3 en Atenci\u00f3 Prim\u00e0ria Jordi Gol (IDIAP Jordi Gol), Mare de D\u00e9u de Guadalupe 2, Planta 1\u00aa, Matar\u00f3, 08303 Barcelona, Spain"},{"name":"Faculty of Medicine, University of Vic-Central University of Vic (UVic-UCC), Catalonia, 08500 Vic, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4854-5934","authenticated-orcid":false,"given":"Gema","family":"Fern\u00e1ndez-Rivas","sequence":"additional","affiliation":[{"name":"Clinical Laboratory North Metropolitan Area, Microbiology Department, Germans Trias i Pujol University Hospital, 08916 Badalona, Spain"},{"name":"Department of Genetics and Microbiology, Autonomous University of Barcelona, 08916 Badalona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Marc","family":"Boigu\u00e9s","sequence":"additional","affiliation":[{"name":"Germans Trias i Pujol Research Institute (IGTP), 08916 Badalona, Spain"},{"name":"Immunology Department, Federation of Clinical Immunology Societies Center of Excellence, Universitat Aut\u00f2noma de Barcelona, 08913 Cerdanyola del Vall\u00e8s, Spain"},{"name":"Laboratori Clinic Metropolitana Nord, Immunology Division, Hospital Universitari Germans Trias i Pujol, 08916 Badalona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mar","family":"Isnard","sequence":"additional","affiliation":[{"name":"Direcci\u00f3 d\u2019atenci\u00f3 Prim\u00e0ria Metropolitana Nord, Institut Catal\u00e0 de la Salut, Sabadell, 08204 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1689-9017","authenticated-orcid":false,"given":"Nuria","family":"Prat","sequence":"additional","affiliation":[{"name":"Direcci\u00f3 d\u2019atenci\u00f3 Prim\u00e0ria Metropolitana Nord, Institut Catal\u00e0 de la Salut, Sabadell, 08204 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0907-9168","authenticated-orcid":false,"given":"Meritxell","family":"Carmona-Cervell\u00f3","sequence":"additional","affiliation":[{"name":"Unitat de Suport a la Recerca Metropolitana Nord, Institut Universitari d\u2019Investigaci\u00f3 en Atenci\u00f3 Prim\u00e0ria Jordi Gol (IDIAP Jordi Gol), Mare de D\u00e9u de Guadalupe 2, Planta 1\u00aa, Matar\u00f3, 08303 Barcelona, 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Barcelona, Spain"},{"name":"Faculty of Medicine, University of Girona, 17071 Girona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,7,9]]},"reference":[{"key":"ref_1","unstructured":"European Centre for Disease Prevention and Control (ECDC) SARS-CoV-2 Variants of Concern as of 28 February 2025. 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