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, states,
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 which 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)
It should be noted that the only time the precious blood may be reserved is when it is to be taken to the sick. It may not be reserved at other times but must be consumed after Mass. It should also be noted that there is no obligation to receive under the form of bread if one is not sick. So long as Communion under the form of wine is being offered to the faithful, they may receive under the form of wine alone.