Purpose: COViK - a prospective hospital-based multicenter case-control study in Germany - aims to assess the effectiveness of COVID-19 vaccines against severe disease. Here, we report vaccine effectiveness (VE) against COVID-19-caused hospitalization and intensive care treatment during the Omicron wave. Methods: We analyzed data from 276 cases with COVID-19 and 494 control patients recruited in 13 hospitals from 1 December 2021 to 5 September 2022. We calculated crude and confounder-adjusted VE estimates. Results: 21% of cases (57/276) were not vaccinated, compared to 5% of controls (26/494; p < 0.001). Confounder-adjusted VE against COVID-19-caused hospitalization was 55.4% (95% CI: 12-78%), 81.5% (95% CI: 68-90%) and 95.6% (95% CI: 88-99%) after two, three and four vaccine doses, respectively. VE against hospitalization due to COVID-19 remained stable up to one year after three vaccine doses. Conclusion: Three vaccine doses remained highly effective in preventing severe disease and this protection was sustained; a fourth dose further increased protection.

We included 852 patients in a prospectively recruiting multicenter matched case-control study in Germany to assess vaccine effectiveness (VE) in preventing COVID-19-associated hospitalization (Delta-variant dominance). Two-dose VE was 89% (95%CI 84-93%) overall, 79% in patients with >2 comorbidities and 77% in adults aged 60-75 years. A third dose increased VE to >93% in all patient-subgroups.

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