96 They are mistaken in appealing in this matter to the social character of the eucharistic sacrifice, for as often as a priest repeats what the divine Redeemer did at the Last Supper, the sacrifice is really completed. Moreover, this sacrifice, necessarily and of its very nature, has always and everywhere the character of a public and social act, inasmuch as he who offers it acts in the name of Christ and of the faithful, whose Head is the divine Redeemer, and he offers it to God for the holy Catholic Church, and for the living and the dead. This is undoubtedly so, whether the faithful are present - as we desire and commend them to be in great numbers and with devotion - or are not present, since it is in no wise required that the people ratify what the sacred minister has done.
Source: Mediator Dei (Vatican.va)