Vance, who's formally leading the U.S. delegation, will be accompanied by second lady Usha Vance, Secretary of State Marco Rubio, and his wife, Jeanette Rubio.
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Both Vance and Rubio are Catholic, and Vance's office says he's the first Catholic convert to be vice president.
Vance met Pope Francis, the current pope's predecessor, shortly before the pontiff's death April 21.
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