With vaccination starting, I think this will die away.

There's a lot of words being used with this 
meaning now but most contain either ワクチン or 
接種. (no specific expression seems to dominate 
just yet)

We're still at a stage where "immunity passport"/"免疫パスポート" is put in quotation marks every time it appears in print. All sorts of new terms are being coined and used by the media during this pandemic. I don't think we need to add them just because they're common, especially when the meaning is easy to derive, as is the case here. I believe we should be more selective about which ones we include while the pandemic is ongoing. We can always add them later.

I'm making sure the word "ephemeral" is somewhere in a comment, as we can search for them.

I think it's perfectly OK to have even if it just describes an idea (wouldn't be the first such entry).