Senti. If there was an efficacy IA some time in 2015 ( and I think there probably was, because the protocol planned for one), it is only the DMC who would see the unblinded data, not NWBO. The DMC is unblinded at all their meetings, mainly to allow for monitoring of comparative safety.
At an efficacy IA, the DMC on the basis of their unblinded look, would simply recommend continue, halt for efficacy, or halt for futility.
Sometimes a company will consider a simple continue rec to be quite a big blow (or their shareholders might).
It all depends on prior expectations before the IA.
If you want to steal a march on competitors by expecting your interim data to allow you to stop early for efficacy, thereby potentially getting to market years early, then receiving a continue rec will be a considerable setback, as was the case recently with Toca, when a continue rec knocked 30% of the share price.
It would be perfectly normal and acceptable for the sponsor to see aggregate event rates, thus allowing them to estimate trial duration and undertake other future planning. And the sponsor will often be able to make reasonable deductions based on those stats.
Unexpected and unplanned events can always happen (protocol violations for example), and might require consultation with the FDA. So such an event may come to the attention of the DMC first, but then involve discussion with the Sponsor and the FDA.
Indeed a major protocol violation could lead to the FDA slapping in a hold, but could be entirely unrelated to actual interim efficacy findings.
