From the Archdiocese of Boston:

In Effect from December 18, 2021 through January 17, 2022

In the light of spiking numbers of new COVID cases and the likely increase in those numbers in the upcoming holiday season, Cardinal Seán is mandating that throughout the archdiocese all people attending public Masses, including weddings and funerals, wear masks.  This mandate takes effect the weekend of December 18/19, 2021, and expires on January 17, 2022.