From Dalkey Archive Press:
On Christmas Eve 1999, all the Jews in the world die in a strange, millennial plague, with the exception of the firstborn males, who are soon adopted by a cabal of powerful people in the American government. By the following Passover, however, only one is still alive: Benjamin Israelien; a kindly, innocent, ignorant man-child. As he finds himself transformed into an international superstar, Jewishness becomes all the rage: matzo-ball soup is in every bowl, sidelocks are hip; and the only truly Jewish Jew left is increasingly stigmatized for not being religious. Since his very existence exposes the illegitimacy of the newly converted, Israelien becomes the object of a worldwide hunt...Also, the title, Witz, is Yiddish for 'joke'.
Meanwhile, in the not-too-distant future of our own, "real" world, another last Jew—the last living Holocaust survivor—sits alone in a snowbound Manhattan, providing a final melancholy witness to his experiences in the form of the punch lines to half-remembered jokes.