The priest is required to receive both the Body and the Blood (the host and the chalice).
The lay members of the congregation aren’t actually required to receive Holy Communion at all, if they don’t want to, or if they are not properly disposed to receive, for any reason.
Jesus is fully present under the appearances of both species, so lay members [assuming they are Catholic, have been trained and educated in classes for First Holy Communion, are free of mortal sin, as undistracted as can reasonably be expected, and having fasted for at least one hour beforehand,] are free to receive either the Host or the Chalice, or both.
Some people are allergic to the accidents of the bread, others may have health reasons for avoiding the Chalice, and still others may appreciate the sign value of receiving both, so the Church provides all three options.
There are times and places where offering the Chalice exposes it to danger from profanation (for example, if the congregation is not trained on how to receive it correctly, or if the parish is one of those that is often visited by alcoholics who are not yet recovering alcoholics,) then they would choose not to offer the Chalice to the congregation, so that no accidents or unfortunate events could occur.
This is possible to do because we receive Jesus alive and entire under the appearance of the Host alone, as well as when we receive both.