Vaccine efficacy VS Covid vaccine mutation

So far I've heard 2 interpretations of why the data coming out of Israel seems to show the Covid vaccines are starting to fail.

1. The Pfizer vaccine is losing its effectiveness.

2. Covid has mutated as viruses do and Delta is no longer stopped by the mRNA vaccine. If we continue to see Covid outbreaks even among those with a 3rd shot/booster then this seems more likely.

Add to this that the IFR for Delta is .08%. I'm wondering if this is the IFR for the Delta virus regardless with whether a person has been vaccinated or not.  I'm also wondering if I'm using all this terminology correctly because I've  ony had a crash course