It is a 3-dose protein vaccine. [1]
"The second of these candidates and the fourth from Cuba uses yeast as a receptor binding domain protein and alumina as an adjuvant." [2]
I suspect there is a translation issue here. I would hope this means they are recombinantly expressing some portion of the RBD in yeast, not that they are using yeast as a vector.
[1] https://www.nytimes.com/2021/06/22/world/americas/cuba-vacci...