After one recites Kiddush, either he or somebody else who heard the Kiddush must drink at least a Rebi’it (approximately 3.1 oz.) of the wine in the cup. This is the ruling of the Shulhan Aruch (Orah Haim 271). If nobody drinks this amount, then the Misva of Kiddush has not been fulfilled. Sometimes, the person who recites Kiddush takes a small sip from the cup and then passes it around. This is incorrect. Somebody has to drink a Rebi’it from the cup, as otherwise the Kiddush is meaningless and the Misva is not fulfilled.
It is preferable for the person who recited Kiddush to drink a Rebi’it. However, if he cannot drink this much wine, for whatever reason, then he may give the cup to somebody else to drink. It is advisable to measure 3.1 oz. before Shabbat in order to determine the minimum amount that must be drunk.
There is no requirement for the others at the table to drink from the Kiddush wine. As long as somebody drinks a Rebi’it from the Kiddush cup, everyone who heard the Kiddush recitation has fulfilled his or her Misva, and there is no need for anybody to drink. If the others at the table have wine in front of them, as is customary, they may not drink until after the one who recited Kiddush – or somebody else – drinks a Rebi’it from the Kiddush cup. Since the Misva is not fulfilled until a Rebi’it is drunk, nobody may drink until that point. However, if the people around the table have a Rebi’it of wine in their cups (as is the custom at the Seder of Pesah, but less common on other occasions), then they may use their cups as Kiddush cups and drink without waiting for the person reciting Kiddush to drink. Generally, though, people have only a small amount of wine in their cups during Kiddush, and in such a case, as mentioned, they must wait until somebody drinks a Rebi’it of the Kiddush wine before drinking.
Earlier in Shulhan Aruch (170), Maran writes that one should not pass onto somebody else a cup from which he had drunk, due to hygienic concerns. Therefore, it is improper to drink from the Kiddush cup after somebody had drunk from it. If one wishes to drink from the Kiddush cup after somebody else had drunk from it, he should pour from the cup into another cup. However, as mentioned, there is no Halachic requirement whatsoever to drink the Kiddush wine once somebody drank a Rebi’it.
Summary: After the recitation of Kiddush, the one who recited Kiddush should drink a Rebi’it (3.1 oz.) of the wine. If he cannot drink this amount, he may have somebody else drink it in his place. Nobody else at the table may drink their wine before somebody drinks a Rebi’it from the Kiddush wine, unless the people at the table have a cup with a Rebi’it of wine. Once somebody drank a Rebi’it of Kiddush wine, there is no requirement at all for anybody else to drink from the Kiddush wine.
