In San Francisco, two (so far) for 13 performances: Michael Fabiano and Giorgio Berrugi.
At the Met, they'll let us know at the end of the run: Charles Castronovo, who was scheduled to sing tonight and November 28, is ill. Perhaps he has whatever has knocked Ramon Vargas out. Francesco Demuro, who was supposed to make his Met debut singing Alfredo next month, will make his debut tonight as Rodolfo instead.
(Demuo has appeared here in Rigoletto, Cosi fan tutte, and Falstaff. He was best in Cosi, and I sure hope Frizza keeps the orchestra down for him.)