Why's there no vaccine against Respiratory Syncytial Virus (RSV)?
In answer to the specific question,
This paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3741363/ is the one the review was talking about.

The epitope that is targeted (the F protein) varies between strains, so a produced vaccine would only work on that strain. The protein (an obvious vaccine target) was selected because it exists on all strains, and is needed for the virion to fuse with the human cell.

In the vaccine The F protein epitope is fused with an immunostimulatory particle to get a good immune response. That's why they mention "prefusion" and "postfusion". There is confusion in the terminology because the F protein is so-named because of its role in fusing the virion to the cell.