(I apologize in advance if this sounds a little rambling. I'm still waking up, lol)
It really only sounds like they released a very, very top-line summary of some first interpret-able results. It's really nothing to write home about or draw sweeping conclusions because we simply have nothing to look at. Let's calm down and wait for the full data to come out publicly. These trials generate loads of data that need to be analyzed by statisticians, while they also package the data for regulatory submission.
At the end of the day, the main pieces of data to look at will be the primary endpoint within the entire population, then look at how efficacy might have varied across stratification groups (they'll often stratify the trial by geographic region and one or two other factors, to look for consistency in these key groups), then look at safety across the trial. These subgroup analyses, which is effectively what this half-dose group is, are just interesting hypothesis-generating items or confirmatory for the primary endpoint. These trials are likely not powered to draw statistically meaningful conclusions from small subgroups. And we definitely cannot draw any meaningful conclusions from post hoc analyses of clinical trial data (as that really amounts to statistical fishing).