Effectiveness of ChAdOx1 nCoV-19 vaccine against SARS-CoV-2 infection during the delta (B.1.617.2) variant surge in India: a test-negative, case-control study and a mechanistic study of post-vaccination immune responses thelancet.com - get the latest breaking news, showbiz & celebrity photos, sport news & rumours, viral videos and top stories from thelancet.com Daily Mail and Mail on Sunday newspapers.