Clinical outcomes in vaccinated and unvaccinated patients with COVID-19: a population-based analysis

O. Papaioannou, T. Karampitsakos, P. Tsiri, V. Sotiropoulou, E. Koulousousa, P. Tasiopoulos, G. Schinas, M. Katsaras, E. Zarkadi, E. Malakounidou, V. Georgiopoulou, F. Sampsonas, A. Spyridonidis, K. Akinosoglou, M. Marangos, A. Tzouvelekis

Department of Respiratory Medicine, Department of Internal Medicine, Department of Hematology, University Hospital of Patras, Patras, Greece. atzouvelekis@upatras.gr

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• Infectious Diseases

OBJECTIVE: Real-life data for vaccination against COVID-19 are sorely needed. This was a population-based analysis aiming at investigating the hospitalization risk for COVID-19 of 98,982 subjects and compare features of vaccinated and unvaccinated patients.

PATIENTS AND METHODS: Hospitalized patients with COVID-19 between 01/07/2021 and 11/02/2022 were included in the study.

RESULTS: 582 patients were included in the analysis [males: 58.6% (n=341), vaccinated patients: 28.5% (n=166), unvaccinated patients: 71.5% (n=416)]. Median age of vaccinated patients was significantly higher compared to median age of unvaccinated [74.0 (95% CI: 72.0-77.0) vs. 59.0 (95% CI: 57.0-62.0), p=0.0001]. Mean latency time (±SD) from the second dose to hospitalization was 5.7±2.6 months. Between 01/07/2021 and 01/12/2021, unvaccinated subjects had higher risk for hospitalization compared to vaccinated [HR: 2.82, 95% CI: 2.30-3.45, p<0.0001]. Between 02/12/2021 and 11/02/2022, unvaccinated subjects presented with higher risk for hospitalization than subjects that had received booster dose [HR: 2.07, 95% CI: 1.44-2.98, p=0.005], but not than subjects that got two doses. Median value of hospitalization days was higher in unvaccinated patients compared to vaccinated [7.0 (95% CI: 7.0-8.0) vs. 6.0 (95% CI: 5.0-7.0), p=0.02]. Finally, age-adjusted analysis showed that hospitalized unvaccinated patients presented with significantly higher mortality risk compared to hospitalized vaccinated patients [HR: 2.59, 95% CI: 1.69-3.98, p<0.0001].

CONCLUSIONS: Vaccination against COVID-19 remains the best way to contain the pandemic. There is an amenable need for booster dose during the omicron era.

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