The studies, which are based on the real-world use of the vaccine in Qatar and Israel, suggest that the vaccine can prevent the worst outcomes — including severe pneumonia and death — caused by B.1.1.7, the variant first identified in the U.K., and B.1.351, the variant first identified in South Africa. “This is really good news,” said Dr. Annelies Wilder-Smith, an infectious disease researcher at the London School of Hygiene and Tropical Medicine. “At this point in time we can confidently say that we can use this vaccine, even in the presence of circulating variants of concern.”... In multiple analyses, the researchers found that the vaccine was 87 to 89.5 percent effective at preventing infection with B.1.1.7 among people who were at least two weeks past their second shot. It was 72.1 to 75 percent effective at preventing infection with B.1.351 among those who had reached the two-week point. Even that slightly reduced effectiveness against infection with B.1.351 is still largely good news, one of the study’s authors, Laith Abu-Raddad, an infectious disease epidemiologist at Weill Cornell Medicine-Qatar, said. “We’re talking about a variant which is probably the nastiest of all the variants of concern,” he said. “It’s not the 95 percent we were hoping, but the 75 percent is really great.”