Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant.

Abstract (PubMed)

BACKGROUND: The B.1.617.2 (delta) variant of SARS-CoV-2 has contributed to a surge in cases in India and has now been detected across the globe. The effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against this variant has been unclear. METHODS: We used a test-negative case-control design to estimate the effectiveness of vaccination against symptomatic disease caused by the delta variant or the alpha variant (B.1.1.7) over the period that the delta variant began circulating. Variants were identified with sequencing and on the basis of the spike gene target status. RESULTS: Effectiveness after one dose was notably lower among persons with delta (30.7%; 95% CI, 25.2 to 35.7) than alpha (48.7%; 95% CI, 45.5 to 51.7). Effectiveness of two doses of BNT162b2 was 93.7% (95% CI, 91.6 to 95.3) against alpha and 88.0% (95% CI, 85.3 to 90.1) against delta. Effectiveness of two doses of ChAdOx1 was 74.5% (95% CI, 68.4 to 79.4) against alpha and 67.0% (95% CI, 61.3 to 71.8) against delta. CONCLUSIONS: Two doses of either vaccine provided substantial protection against symptomatic disease with the delta variant.