The results are all the more striking, experts said, because Israel is contending with a worrisome new variant of the coronavirus. The variant B.1.1.7 now accounts for up to 80 percent of the samples tested in Israel. First identified in Britain in December, the variant has spread to 72 other countries and may be up to 50 percent more transmissible than other variants. Israel leads the world in vaccinating its citizens. So far, more than a third of its population of more than nine million people has received a first dose of the Pfizer-BioNTech vaccine and nearly two million people have received a second dose.