Vaccine effectiveness against infection with the Delta (B.1.617.2) variant, Norway, April to August 2021

Some variants of SARS-CoV-2 are associated with increased transmissibility, increased disease sever-ity or decreased vaccine effectiveness (VE). In this population-based cohort study (n = 4,204,859), the Delta variant was identified in 5,430 (0.13%) indi-viduals, of whom 84 were admitted to hospital. VE against laboratory confirmed infection with the Delta variant was 22.4% among partly vaccinated (95% confidence interval (CI): 17.0-27.4) and 64.6% (95% CI: 60.6-68.2) among fully vaccinated individuals, compared with 54.5% (95% CI: 50.4-58.3) and 84.4% (95%CI: 81.8-86.5) against the Alpha variant.

Automated summary

This population-based cohort study found that the vaccine effectiveness against the Delta variant was significantly lower for partially vaccinated individuals at 22.4% compared to 64.6% for fully vaccinated individuals, when compared to vaccine effectiveness against the Alpha variant at 54.5% and 84.4% respectively.