The results also showed associations between the risk of severe disease and clinical characteristics such as higher age, history of diabetes, lymphocytopenia, thrombocytopenia, elevated LDH (lactate dehydrogenase), and elevated CRP (C-reactive protein). Notably, age was also found to be an important predictor of more severe disease in COVID-19 patients, even in those with a breakthrough infection.

The researchers noted that observed differences in clinical characteristics may reflect differences in vaccination priorities based on underlying comorbidities. During the study period, high-risk groups, such as individuals over 65 years old, health care workers and people with disabilities were priority targets for COVID-19 vaccination. Therefore, elderly patients and patients with at least one comorbidity were more common in the vaccinated group than in unvaccinated group in the study.


“Despite these differences, mechanical ventilation and in-hospital death occurred only in the unvaccinated group,” Dr. Jeong said. “Furthermore, after adjusting for baseline clinical characteristics, analysis showed that fully vaccinated patients were at significantly lower risk of requiring supplemental oxygen and of ICU admission than unvaccinated patients.”

Although additional research will be needed as different variants emerge, this study sheds light on the clinical effectiveness of COVID-19 vaccination in the context of breakthrough infections.


RSNA is an association of radiologists, radiation oncologists, medical physicists and related scientists promoting excellence in patient care and health care delivery through education, research and technologic innovation. The Society is based in Oak Brook, Illinois.

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