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Importance: With a large proportion of the US adult population vaccinated against SARS-CoV-2, it is important to identify who remains at risk of severe disease in the event of infection.Objective: To characterize risk factors for severe COVID-19 disease in a vaccinated population.Design: Nationwide, retrospective cohort study.Setting: US Department of Veterans Affairs Hospitals.Participants: US Veteran patients who received a COVID-19 vaccination series and later developed a laboratory-confirmed SARS-CoV-2 infection.Exposures: Demographics, comorbidities, immunocompromised states, and vaccination-related variables.Main Outcome and Measures: Development of severe versus non-severe COVID-19 disease. Severe disease was defined as hospitalization within 14 days of a positive SARS-CoV-2 diagnostic test and either SpO2 < 94%, receipt of supplemental oxygen or dexamethasone, mechanical ventilation, or death within 28 days.Results: Among 110,760 patients with breakthrough infections, 10,612 (9.6%) had severe COVID-19 or died within 28 days of the COVID-19 diagnosis. The strongest risk factor for severe disease despite vaccination was age, which increased with every 5-year increase in age > 50 (approximate adjusted odds ratio (aOR), 1.5). Risk among patients ≥ 80 years old was particularly high (aOR 16.1, CI 13.1 – 19.9, relative to patients 45-50 years old. Immunocompromising conditions, including receipt of different classes of immunosuppressive medications (aORs 1.73 – 2.44, CIs 1.37 – 2.99) or cytotoxic chemotherapy (aOR 2.69, CI 2.25 – 3.21) prior to breakthrough infection, or leukemias/lymphomas (aOR 1.84, CI 1.59 – 2.14) and chronic conditions associated with end-organ disease, such as heart failure, dementia, and chronic kidney disease, were also associated with increased risk. Receipt of an additional (booster) dose of vaccine was associated with reduced odds of severe disease.Conclusions and Relevance: In this nationwide, retrospective cohort of US Veterans, we identified risk factors for severe disease despite vaccination. Findings could be used to inform outreach efforts for booster vaccinations and to inform clinical decision making about identifying patients who might benefit from pre-exposure prophylaxis and antiviral therapy. |
