BACKGROUND: The Omicron variant of SARS-CoV-2 evades immunity conferred by vaccines and previous infections. METHODS: We used a Cox proportional hazards model and a logistic regression on individual-level population-wide data from the Czech Republic to estimate risks of infection and hospitalization, including severe states. RESULTS: A recent (≤ 2 months) full vaccination reached VE 43% (95% CI: 42-44) against infection by Omicron compared to 73% (CI: 72-74) against Delta. A recent booster increased VE to 56% (CI: 55-56) against Omicron infection compared to 90% (CI: 90-91) for Delta. The VE against Omicron hospitalization of a recent full vaccination was 45% (95% CI: 29-57), with a recent booster 87% (CI: 84-88). The VE against the need for oxygen therapy due to Omicron was 57% (CI: 32-72) for recent vaccination, 90% (CI: 87-92) for a recent booster. Post-infection protection against Omicron hospitalization declined from 68% (CI: 68-69) at ≤ 6 months to 13% (CI: 11-14) at > 6 months after a previous infection. The OR for Omicron relative to Delta was 0.36 (CI: 0.34-0.38) for hospitalization, 0.24 (CI: 0.22-0.26) for oxygen, and 0.24 (CI: 0.21-0.28) for ICU admission. DISCUSSION: Recent vaccination still brings substantial protection against severe outcome for Omicron.
Protection by vaccines and previous infection against the Omicron variant of SARS-CoV-2