Effectiveness of COVID-19 vaccines against SARS-CoV-2 infection with the Delta (B.1.617.2) variant: second interim results of a living systematic review and meta-analysis, 1 January to 25 August 2021

The Delta variant has become the dominant strain of SARS-CoV-2. We summarised the evidence on COVID-19 vaccine effectiveness (VE) identified in 17 studies that investigated VE against different endpoints. Pooled VE was 63.1% (95% confidence interval (CI): 40.9-76.9) against asymptomatic infection, 75.7% (95% CI: 69.3-80.8) against symptomatic infection and 90.9% (95% CI: 84.5-94.7) against hospitalisation. Compared with the Alpha variant, VE against mild outcomes was reduced by 10-20%, but fully maintained against severe COVID-19.

Automated summary

Research shows that COVID-19 vaccines are effective in preventing various degrees of infection, with efficacy rates of 63.1%, 75.7%, and 90.9% against asymptomatic infection, symptomatic infection, and hospitalization, respectively. Compared to the Alpha variant, the efficacy against mild outcomes is slightly reduced by 10-20%, but remains fully maintained against severe COVID-19.