Effectiveness of COVID-19 vaccines against SARSCoV-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

Abstract

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. The Delta variant (Phylogenetic Assignment of Named Global Outbreak (Pango) lineage designation B.1.617.2) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in October 2020 and has spread to more than 180 countries globally [1]. Concerns were raised about how well the currently available vaccines protect against this variant. Since January 2021, the Robert Koch Institute (RKI), in collaboration with the National Immunisation Technical Advisory Groups (NITAGs) network coordinated by the European Centre for Disease Prevention and Control (ECDC) is performing a living systematic review on the efficacy, effectiveness and safety of coronavirus disease (COVID-19) vaccines authorised in the European Union (EU) (PROSPERO registration: CRD42020208935) [2]. Here we present results on the effectiveness and the duration of protection provided by the EU-licensed COVID-19 vaccines in respect to the Delta variant.