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.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of observational vaccine effectiveness studies
PubMed 34651577 · doi:10.2807/1560-7917.ES.2021.26.41.2100920
What was done
Second interim results of a living systematic review and meta-analysis investigating COVID-19 vaccine effectiveness against the SARS-CoV-2 Delta (B.1.617.2) variant across 17 studies identified between 1 January and 25 August 2021.
What was found
Pooled vaccine effectiveness against the Delta variant was 63.1% (95% CI: 40.9–76.9) for asymptomatic infection, 75.7% (95% CI: 69.3–80.8) for symptomatic infection, and 90.9% (95% CI: 84.5–94.7) for hospitalisation. Compared with the Alpha variant, effectiveness against mild outcomes dropped by 10–20% but was fully maintained against severe COVID-19.
Why it matters
Demonstrates that COVID-19 vaccination preserved high protection against severe disease requiring hospitalisation during the Delta surge, despite reduced protection against mild and asymptomatic infections.
Limits
The abstract lacks details on total sample size, specific vaccine products, dose numbers, waning over time, and heterogeneity across the 17 included observational studies.
Cited by
- supports With the Delta variant, COVID-19 vaccine effectiveness against transmission decreased compared to earlier in the pandemic, but protection against hospitalization and severe disease remained largely preserved.