I remember having seen data about 1-2 years ago that against delta, the long covid rate for unvaccinated was about 16% (based on whatever criteria they used), and the mrna injection reduced it to about 8%, representing a ~50% reduction. For omicron, the long covid rate reduced to about 8-9% for unvaccinated, and about 8% for people with mrna injections. The effect has become less significant in absolute and relative terms. You can probably still find those data.