It's pretty clear information that cortisone lowers the immune function. All I can tell you is that if it was me, I would try everything else first.
Personally, I won't accept steroids for inflammation under any circumstances for the rest of my life, unless I'm in danger of losing my life from it, but I've been battling these infections nearly all my life, so my circumstances may be different than yours.
And new articles have come out about
the outcomes when steroids are used for bell's palsy:
https://www.sciencedaily.com/releases/2016/09/160906182119.htm