May sick persons who are unable to swallow solid food receive Communion under the form of wine alone?
Yes, and so may anyone. The U.S. bishops’ document This Holy and Living Sacrifice, which was approved by the Holy See, says,
Sick people who are unable to receive Communion under the form of bread may receive it under the form of wine alone. If the wine is consecrated at a Mass not celebrated in the presence of the sick person, the blood of the Lord is kept in a properly covered vessel and is placed in the tabernacle after Communion. The precious blood should be carried to the sick in a vessel that is closed in such a way as to eliminate all danger of spilling. If some of the precious blood remains, it should be consumed by the minister, who should also see to it that the vessel is properly purified. (HLS 37)
The only time the precious blood may be reserved is when it is to be taken to the sick. It should also be noted that there is no obligation, even if one is not sick, to receive under the form of bread. When both forms are offered, one may receive under the form of wine alone.