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Background <p>To characterize real-world COVID-19 vaccine-induced protection, we assessed breakthrough infections and protective antibody thresholds among fully vaccinated nursing home residents (NHR) and staff (NHS).</p> Methods <p>We conducted a cohort study to assess infection rates and risk factors of symptomatic breakthrough infections in 1605 NHR and 1200 NHS (2021) and 483 NHR (2022) in Belgium using multivariable Cox proportional hazards models adjusted for potential confounders. Additionally, a case-control analysis was used to compare pre-infection and peak vaccine response antibody levels between breakthrough cases and matched controls. Receiver Operating Characteristic (ROC) and net benefit models were fitted to evaluate the protective antibody thresholds in clinical decision making.</p> Results <p>In 2021, breakthrough infection incidence was 10.7 (95%CI 8.6–13.2) per 100 person-years in NHS and 2.4 (95%CI 1.59–3.46) in NHR. This rose to 10.6 (95%CI 8.3–13.3) in NHR in 2022. Prior infection was protective in NHS (hazard ratio (HR) 0.25, 95%CI 0.13–0.46) and NHR (HR 0.2, 95%CI 0.05–0.87). In NHS, younger age (HR 1.02, 95%CI 1.01–1.04) and Delta circulation (HR 9.52, 95%CI 2.65–34.21) and in NHR, Omicron BA.5 circulation (HR 17.95, 95%CI 2.35-137.13) increased infection risk. Breakthrough cases had lower pre-infection and peak vaccine antibody levels than controls. Protective antibody thresholds were identified and were higher for infections during Omicron than Delta. Using these antibody thresholds to guide vaccination adds value at low risk thresholds, though net benefits were modest.</p> Conclusion <p>Breakthrough infections affected a minority of vaccinated NHR and NHS. Risk depended on age, prior infection, and circulating variants. Lower antibody levels in cases support their protective role, though thresholds are variant-specific. Our findings support tailored vaccine strategies in this vulnerable population.</p>

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SARS-CoV-2 breakthrough infection incidence, risk factors, and antibody correlates in Belgian nursing homes residents and staff (2021–2022)

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月24日

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  • Liselore De Rop,
  • Eline Meyers,
  • Natalja Van Biesen,
  • Tine De Burghgraeve,
  • Marina Digregorio,
  • Anja Coen,
  • Nele De Clercq,
  • Laëtitia Buret,
  • Samuel Coenen,
  • Els Duysburgh,
  • Beatrice Scholtes,
  • Piet Cools,
  • Stefan Heytens,
  • Jan Y Verbakel

摘要

Background

To characterize real-world COVID-19 vaccine-induced protection, we assessed breakthrough infections and protective antibody thresholds among fully vaccinated nursing home residents (NHR) and staff (NHS).

Methods

We conducted a cohort study to assess infection rates and risk factors of symptomatic breakthrough infections in 1605 NHR and 1200 NHS (2021) and 483 NHR (2022) in Belgium using multivariable Cox proportional hazards models adjusted for potential confounders. Additionally, a case-control analysis was used to compare pre-infection and peak vaccine response antibody levels between breakthrough cases and matched controls. Receiver Operating Characteristic (ROC) and net benefit models were fitted to evaluate the protective antibody thresholds in clinical decision making.

Results

In 2021, breakthrough infection incidence was 10.7 (95%CI 8.6–13.2) per 100 person-years in NHS and 2.4 (95%CI 1.59–3.46) in NHR. This rose to 10.6 (95%CI 8.3–13.3) in NHR in 2022. Prior infection was protective in NHS (hazard ratio (HR) 0.25, 95%CI 0.13–0.46) and NHR (HR 0.2, 95%CI 0.05–0.87). In NHS, younger age (HR 1.02, 95%CI 1.01–1.04) and Delta circulation (HR 9.52, 95%CI 2.65–34.21) and in NHR, Omicron BA.5 circulation (HR 17.95, 95%CI 2.35-137.13) increased infection risk. Breakthrough cases had lower pre-infection and peak vaccine antibody levels than controls. Protective antibody thresholds were identified and were higher for infections during Omicron than Delta. Using these antibody thresholds to guide vaccination adds value at low risk thresholds, though net benefits were modest.

Conclusion

Breakthrough infections affected a minority of vaccinated NHR and NHS. Risk depended on age, prior infection, and circulating variants. Lower antibody levels in cases support their protective role, though thresholds are variant-specific. Our findings support tailored vaccine strategies in this vulnerable population.