These are fair questions. I guess I'd first say that there were studies on reactogenic/immunogenic effects coincident w/ the original rollout. But perhaps more importantly, this study conditions on the time frame, meaning that it applies to all participants, and should thus not affect the risk ratio. I think knowing the current hazard risk ratio is more scientifically/medically valuable than the previous one (even if I'm skeptical that it has changed significantly for reasons other than noise)