I don't know all the details but it was 28% of people who were not doing particularly well with tapering off prednisone.

"The approval of sarilumab for PMR was based on findings from the phase 3 SAPHYR clinical trial for patients with steroid-resistant active PMR who flared on ≥7.5 mg/day prednisone or equivalent during taper."

https://www.ajmc.com/view/sarilumab-indication-expanded-to-include-polymyalgia-rheumatica
No medication comes with a guarantee that it will work 100% for everyone. There is also no guarantee that people won't have side effects on Kevzara. The nice thing is Kevzara can be stopped if it doesn't work or if people have side effects.

Prednisone is very difficult to stop even when people experience side effects. It might be good to have an alternative to prednisone.