Protection by Vaccines and Previous Infection Against the Omicron Variant of Severe Acute Respiratory Syndrome Coronavirus 2
Abstract
Effectiveness of vaccines and postinfection immunity against the Omicron variant of SARS-CoV-2 is significantly lower than against the Delta variant. The probability of a severe outcome is substantially lower for the Omicron variant compared to Delta.
Background The Omicron variant of severe acute respiratory syndrome coronavirus 2 (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 (6 months after a previous infection. The odds ratios for Omicron relative to Delta were 0.36 (95% CI, .34-.38) for hospitalization, 0.24 (95% CI, .22-.26) for oxygen, and 0.24 (95% CI, .21-.28) for intensive care unit admission.
Conclusions Recent vaccination still brings substantial protection against severe outcome for Omicron.