In the Ordinariate Mass, as the Priest breaks the Host he says
V Alleluia! Christ our Passover is sacrificed for us.
R Therefore let us keep the feast, Alleluia!
This is derived from a formula in "The Masse" which Cranmer composed for his 1549 Prayer Book. For explanation, let us turn to the Easter Homily of Pope Benedict XVI in 2009:
" Christ our Passover is sacrificed: S Paul's triumphant words ring forth ... It is a text which originated barely twenty years after the death and resurrection of Jesus, and yet - like many Pauline passages - it already contains, in an impressive synthesis, a full awareness of the newness of life in Christ. The central symbol of Salvation History - the Paschal Lamb - is here identified with Jesus, who is called 'our Paschal Lamb'. The Hebrew Passover commemorating the liberation from slavery in Egypt, provided for the ritual sacrifice of a lamb every year, as prescribed in the Mosaic Law. In his passion and death, Jesus reveals himself as the Lamb of God, 'sacrificed' on the Cross, to take away the sins of the world. He was killed at the very hour when it was customary to sacrifice the lambs in the Temple of Jerusalem. The meaning of his sacrifice he had himself anticipated during the Last Supper, substituting himself - under the signs of bread and wine - for the ritual food of the Hebrew Passover meal. Thus we can truly say that Jesus brought to fulfilment the tradition of the ancient Passover, and transformed it into his Passover".
Footnote: the Alleluias are added during Easter. The passage of S Paul is at I Corinthians 5. "For us", not in the earlier manuscripts, is found in the Textus Receptus, the common Greek text of the Middle Ages, but not in the Vulgate Latin.