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Risk factors of COVID-19 breakthrough infection: a case-control test-negative design study
Gabriela Tejada-Panduro1,2, Laia Pinós-Tella3,4, Susana Otero-Romero1,2,5
1Servei de Medicina Preventiva i Epidemiologia, Vall d'Hebron Barcelona Hospital Campus, Vall d'Hebron Hospital Universitari, Passeig Vall d'Hebron 119-129, Barcelona, 08035, Spain.
BMC Infectious Diseases
|October 17, 2025
Summary
Vaccine effectiveness wanes over time, increasing breakthrough SARS-CoV-2 infections. Immunosuppression is a significant risk factor for COVID-19 breakthrough infections in hospitalized patients.
Area of Science:
- Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- Identifying risk factors for breakthrough SARS-CoV-2 infection post-vaccination is crucial for public health strategies.
- Understanding factors influencing vaccine effectiveness is key to managing the COVID-19 pandemic.
Purpose of the Study:
- To identify risk factors for breakthrough SARS-CoV-2 infection in hospitalized patients after receiving at least one dose of a COVID-19 vaccine.
- To assess the impact of time since last vaccination and immunosuppression on breakthrough infections.
Main Methods:
- Case-control test-negative design study involving hospitalized patients with severe acute respiratory infection.
- Matching cases and controls by age and date of SARS-CoV-2 PCR testing.
- Logistic regression analysis to determine adjusted odds ratios for breakthrough infection.
Main Results:
- A total of 1,340 breakthrough SARS-CoV-2 infections were analyzed against 4,016 controls.
- Vaccination more than 6 months prior to hospitalization increased breakthrough infection odds by 64% (aOR 1.64).
- Immunosuppression was strongly associated with breakthrough infection (aOR 2.04).
Conclusions:
- Hospitalized patients with their last vaccine dose over six months prior face a significantly higher probability of breakthrough SARS-CoV-2 infection.
- Immunosuppression emerges as the most critical risk factor for breakthrough SARS-CoV-2 infections.
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