The one who recites Kiddush on Shabbat must not speak at all after he completes the recitation until after he drinks some of the wine. If he did speak before drinking, such as if he wished the people at the table "Shabbat Shalom," then he must repeat the Beracha of "Boreh Peri Ha’gefen" and then drink. The people at the table, however, do not have to recite the Beracha before they drink the wine. By answering "Amen" to his Beracha, they are considered as having themselves recited the Beracha, and therefore, the interruption made by the person who recited Kiddush has no effect on them. They are considered as though they recited the Kiddush, and thus as long as they did not speak before drinking, they may drink without reciting "Boreh Peri Ha’gefen." Although the person who recited Kiddush must repeat "Boreh Peri Ha’gefen," the other people at the table do not.
This is the ruling of several Halachic authorities, including the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909) and the Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933), in Sha’ar Ha’siyun (213).
