Abstract
We estimated vaccine effectiveness (VE) against severe COVID-19 during October 2021, using Slovenian surveillance data. For people fully vaccinated with any vaccine in age groups 18-49, 50-64, ≥ 65 years, VE was 86% (95% CI: 79-90), 89% (85-91), and 77% (74-81). Among ≥ 65 year-olds fully vaccinated with mRNA vaccines, VE decreased from 93% (95% CI: 88-96) in those vaccinated ≤ 3 months ago to 43% (95% CI: 30-54) in those vaccinated ≥ 6 months ago, suggesting the need for early boosters.