Relative vaccine effectiveness (rVE) against COVID-19-related death
rVE estimates showed that additional protection against COVID-19-related death achieved with the first booster decreased over time in both age groups (Table S2, Figure S3), specifically from 61.3% (95%CI: 48.3; 71.0) in April-May 2022 to 34.6% (95%CI: 10.7; 52.1) in October-November 2022 for the ≥80-years and from 66.0% (95%CI: 55.2;74.3) in April-May 2022 to -8.5% (95%CI: -69.6; 30.6) in October-November 2022 for the 65–79-years.
Considering first booster vaccination ≥90 days ago as a reference group, the second booster rVE against COVID-19-related death varied between 58.0% (95%CI: 50.3; 64.5) in June-July 2022 and 65.0% (95%CI: 40.9; 79.3) in October-November 2022 for the ≥80-years. For the 65–79-years the first available estimate of second booster rVE was 74.0% (95%CI: 60.6; 82.8) in October-November 2022 (Table S3, Figure S4).