This year, December 8 is the second Sunday of Advent. Therefore the Solemnity of the Immaculate Conception is transferred to Monday, December 9, which is a holy day of obligation. No vigils are allowed on Sunday, since Advent takes precedence. Click on link below for more clarification from the Archdiocese of Miami.
https://www.miamiarch.org/CatholicDiocese.php?op=Article_solemnity-of-the-immaculate-conception