The study by Lopez Bernal et al. investigates the effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against the B.1.617.2 (Delta) variant of SARS-CoV-2, which has contributed to a surge in cases globally, including in the United Kingdom. Using a test-negative case-control design, the researchers estimated the effectiveness of the vaccines against symptomatic disease caused by the Delta variant compared to the Alpha variant (B.1.1.7). The results show that the effectiveness after one dose of either vaccine was notably lower against the Delta variant (30.7% for BNT162b2 and 30.7% for ChAdOx1 nCoV-19) compared to the Alpha variant (48.7%). However, with two doses, the effectiveness was significantly higher, with BNT162b2 showing 93.7% effectiveness against the Alpha variant and 88.0% against the Delta variant, and ChAdOx1 nCoV-19 showing 74.5% and 67.0%, respectively. The study concludes that while the Delta variant reduces vaccine effectiveness, the differences are modest, and efforts to maximize vaccine uptake with two doses among vulnerable populations remain crucial.The study by Lopez Bernal et al. investigates the effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against the B.1.617.2 (Delta) variant of SARS-CoV-2, which has contributed to a surge in cases globally, including in the United Kingdom. Using a test-negative case-control design, the researchers estimated the effectiveness of the vaccines against symptomatic disease caused by the Delta variant compared to the Alpha variant (B.1.1.7). The results show that the effectiveness after one dose of either vaccine was notably lower against the Delta variant (30.7% for BNT162b2 and 30.7% for ChAdOx1 nCoV-19) compared to the Alpha variant (48.7%). However, with two doses, the effectiveness was significantly higher, with BNT162b2 showing 93.7% effectiveness against the Alpha variant and 88.0% against the Delta variant, and ChAdOx1 nCoV-19 showing 74.5% and 67.0%, respectively. The study concludes that while the Delta variant reduces vaccine effectiveness, the differences are modest, and efforts to maximize vaccine uptake with two doses among vulnerable populations remain crucial.