Increased risk of infection with SARS-CoV-2 Omicron compared to Delta in vaccinated and previously infected individuals, the Netherlands, 22 November to 19 December 2021

Infections by the Omicron SARS-CoV-2 variant are rapidly increasing worldwide. Among 70,983 infected individuals (age ≥ 12 years), we observed an increased risk of S-gene target failure, predictive of the Omicron variant, in fully vaccinated (odds ratio: 5.0; 95% confidence interval: 4.0-6.1) and previously infected individuals (OR: 4.9: 95% CI: 3.1-7.7) compared with infected naïve individuals. This suggests a substantial decrease in protection from vaccine- or infection-induced immunity against SARS-CoV-2 infections caused by the Omicron variant compared with the Delta variant.