Yeah, it's not 100% protection in all studies. One study did have no participants contract aids which is fantastic and would be one data point for 100% prevention.
Another had 2 participants contract HIV out of about 2000 "Person-years". This was compared to another HIV treatment where 9 people contracted HIV (with only 1k "person-years" in that cohort). This equated to 89% reduction in HIV contraction compared to the other PrEP drug.
And that IS a fantastic result and if everyone could take this we'd probably be in a great spot HIV wise. ~90% improvement over current PrEP is great, and it's way easier to take and not mess up.
[1] https://www.askgileadmedical.com/len4prep/understanding/#stu...