{
  "abstract": "Background: Residents of Long-Term Care Facilities (LTCFs) represent a highly vulnerable population characterized by immunosenescence, multimorbidity, and heterogeneous immune responses to repeated SARS-CoV-2 vaccination and infection. Conventional analyses based on single clinical variables often fail to capture this complexity. We evaluated longitudinal humoral immune responses in institutionalized older adults to identify data-driven antibody profiles and characterize cluster-specific waning kinetics.\n\nMethods: In a prospective multicenter cohort of 388 Italian LTCF residents followed across four time points (T0–T3 over 12 months), longitudinal anti-Spike (anti-S) and anti-Nucleocapsid (anti-N) IgG levels were measured alongside demographic and vaccination data. Principal Component Analysis (PCA) was used for dimensionality reduction, followed by K-means clustering. Optimal cluster number was determined using internal validation metrics (Silhouette, Calinski-Harabasz, and Davies-Bouldin indices) and bootstrap stability analysis. Linear mixed-effects models were applied to describe cluster-specific antibody waning trajectories.\n\nResults: A longitudinal analysis was conducted on 388 LTCF residents. Three antibody trajectory profiles emerged: (i) a Vaccine-Driven profile (n = 130), characterized by moderate anti-S titers and progressive antibody decline; (ii) a Hybrid Immunity profile (n = 125), characterized by evidence of prior infection and remarkably stable antibody concentrations throughout follow-up despite limited uptake of the 2023/2024 booster; and (iii) a High-Peak Hybrid Responder profile (n = 133), exhibiting the highest baseline anti-S titers followed by the steepest rate of antibody waning. Across the cohort, 12 of 388 residents (3.1%) developed documented symptomatic SARS-CoV-2 infection during follow-up, with no COVID-19-related deaths and no significant difference in infection incidence among profiles. Bootstrap stability analysis showed a mean Adjusted Rand Index (ARI) of 0.74 (SD 0.20).\n\nConclusion: Unsupervised machine learning effectively resolves the complex heterogeneity of SARS-CoV-2 humoral responses in LTCF residents into data-driven trajectory patterns. These findings illustrate the utility of data-driven approach for describing humoral dynamics while distinguishing observational antibody kinetics from direct estimates of clinical protection.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Cardiovascular, Endocrine-Metabolic Diseases and Aging, Istituto Superiore di Sanità , ,",
    "Department of Infectious Diseases, Istituto Superiore di Sanità , ,",
    "Department of Neurobiology, Care Sciences and Society, Karolinska Institutet and Stockholm University, Aging Research Center , ,",
    "ANASTE Humanitas Foundation , ,",
    "Research Unit of Internal Medicine, Department of Medicine and Surgery, Università Campus Bio-15 Medico , ,",
    "Department of Medical and Surgical Sciences, Hygiene Unit, Policlinico Foggia Hospital, University of Foggia , ,",
    "Unit of Hygiene and Public Health, Department of Cardiac, Thoracic, Vascular Sciences, and Public, University of Padua , ,",
    "Department of Medicine (DIMED), University of Padua , ,",
    "Microbiology and Virology Unit, “Pugliese-Ciaccio” Hospital , ,",
    "Fondazione Policlinico Universitario “Agostino Gemelli” IRCCS , ,"
  ],
  "article_type": "research article",
  "arxiv": null,
  "author_total": 16,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Annapina Palmieri"
    },
    {
      "affs": [
        0
      ],
      "name": "Cecilia Damiano"
    },
    {
      "affs": [
        1
      ],
      "name": "Pasqualina Leone"
    },
    {
      "affs": [
        2
      ],
      "name": "Caterina Trevisan"
    },
    {
      "affs": [
        3
      ],
      "name": "Alba Malara"
    },
    {
      "affs": [
        2
      ],
      "name": "Alberto Zucchelli"
    },
    {
      "affs": [
        4
      ],
      "name": "Raffaele Antonelli Incalzi"
    },
    {
      "affs": [
        5
      ],
      "name": "Rosa Prato"
    },
    {
      "affs": [
        5
      ],
      "name": "Francesca Fortunato"
    },
    {
      "affs": [
        6
      ],
      "name": "Tatjana Baldovin"
    },
    {
      "affs": [
        7
      ],
      "name": "Alessandra Coin"
    },
    {
      "affs": [
        8
      ],
      "name": "Pasquale Minchella"
    },
    {
      "affs": [
        3
      ],
      "name": "Stefania Giordano"
    },
    {
      "affs": [
        1
      ],
      "name": "Anna Teresa Palamara"
    },
    {
      "affs": [
        9
      ],
      "name": "Graziano Onder"
    },
    {
      "affs": [
        1
      ],
      "name": "Giorgio Fedele"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7vmw3vdq4nt1w.bib",
  "cited_by": 0,
  "doi": "10.3389/fragi.2026.1963384",
  "fulltext_url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13724463/?tool=EBI",
  "id": "7vmw3vdq4nt1w",
  "issns": [
    "2673-6217"
  ],
  "landing_url": "https://europepmc.org/article/PMC/PMC13724463",
  "language": "eng",
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "heading",
      "Original Research"
    ],
    [
      "openalex",
      "2725|SARS-CoV-2 and COVID-19 Research"
    ]
  ],
  "openalex": "W7222966717",
  "pdf_url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13724463/pdf/?tool=EBI",
  "pmcid": "PMC13724463",
  "pmid": "42973761",
  "published": "2026-10-19",
  "publisher": "Frontiers Media SA",
  "ris": "https://research.draconitic.com/paper/7vmw3vdq4nt1w.ris",
  "sources": [
    {
      "first_seen": "2026-11-03T15:20:50Z",
      "native_id": "PMC:PMC13724463",
      "source": "europepmc",
      "url": "https://europepmc.org/article/PMC/PMC13724463"
    },
    {
      "first_seen": "2026-11-04T12:23:02Z",
      "native_id": "PMC13724463",
      "source": "pmc",
      "url": "https://doi.org/10.3389/fragi.2026.1963384"
    },
    {
      "first_seen": "2026-11-04T15:20:48Z",
      "native_id": "MED:42973761",
      "source": "europepmc",
      "url": "https://europepmc.org/article/MED/42973761"
    }
  ],
  "subjects": [
    {
      "field": "medicine",
      "origin": "openalex:2725|SARS-CoV-2 and COVID-19 Research",
      "subfield": "infectious-disease"
    }
  ],
  "title": "Longitudinal immune trajectories following SARS-CoV-2 vaccination in long-term care facility residents: an unsupervised analysis approach",
  "title_text": "Longitudinal immune trajectories following SARS-CoV-2 vaccination in long-term care facility residents: an unsupervised analysis approach",
  "type": "peer-reviewed",
  "updated_at": "2026-11-05T12:21:13Z",
  "url": "https://research.draconitic.com/paper/7vmw3vdq4nt1w",
  "venue": "Frontiers in aging",
  "versions": []
}