Rejecting sharp criticism from U.S. government scientists, AstraZeneca said Wednesday night that its Covid-19 vaccine was 76% effective at reducing the risk of symptomatic Covid-19, and 100% effective against severe disease, in a new analysis of its large U.S.-based clinical trial. Those estimates were just a few percentage points lower than much more sparse results the company released Monday from an earlier analysis of the study, despite dramatic statements from government scientists that AstraZeneca’s initial release may have used “outdated information” that could have been overly favorable.