FDA and folks failed to understand immunotherapy and that's why they established PFS as primary. Immune system takes time to work, you may progress initially but eventually tumor may start to shrink over time. How hard is it to understand we have OS like no other. Safety profile - check OS - check PFS - call it check as it must have been at par if not better than SOC.
If vaccine was not working, everyone would not be living longer as everyone witched to treatment arm.