Two studies on the PCSK9 inhibitors evolocumab and alirocumab were recently published in the New England Journal of Medicine (see here and here). See this story by Larry Husten for the details. Evolocumab and alirocumab are monoclonal antibodies that are in development and are seeking FDA approval based on LDL-cholesterol reduction this year.  The two studies were not designed to answer the question of whether evolocumab and alirocumab prevent cardiovascular events. Rather, the studies measured LDL reduction and tabulated adverse events over a 52- or 78-week time period. Among the adverse events being tabulated were cardiovascular events and there were fewer cardiovascular events in the patients who were in the evolocumab and alirocumab groups, as compared to patients who received placebo or usual care. One of the studies had prespecified an exploratory analysis of cardiovascular events. For the other study the investigators did a post hoc analysis of certain cardiovascular events. Neither study was powered (i.e., big and long enough) to provide a reliable estimate of the benefits of these drugs in reducing heart attacks, strokes and deaths. In other words, statistically speaking the studies were pretty thin gruel and the companies as well as the investigators acknowledge that fact. So, as of now, we really do not know that these drugs reduce the risk of cardiovascular events, let alone by how much. Nor do we really know how safe the drugs are. All these studies tell us is that as of now these drugs appear to be progressing satisfactorily along the path to approval and we just have to be patient for a couple of years until the results of the outcomes trials are available.
Fortunately, the sponsors have started large cardiovascular outcomes trials in high risk patients (e.g., the alirocumab trial will involve 18,000 patients and a minimum of 1613 primary endpoint events and a minimum two year followup — see here for a description of the trial).
I suggest taking a look at this short video of Harlan Krumholz speaking from the conference — I completely agree with his comments (website registration may be required). I also agree with the editorial by Donald Lloyd-Jones and Neil Stone, in which they state:

The ODYSSEY LONG TERM and OSLER studies whet our appetites for further results that show cardiovascular benefit and documented safety, even at substantially lower LDL cholesterol ranges than achieved before. However, it would be premature to endorse these drugs for widespread use before the ongoing randomized trials, appropriately powered for primary end-point analysis and safety assessment, are available. Reports from several lipid treatment trials provide important object lessons in this regard. Two trials of niacin revealed lower levels of LDL cholesterol and lipoprotein(a) when niacin was added to statin therapy but no net clinical benefit and very worrisome signals of harm. A randomized, controlled trial of torcetrapib reminds us that “off-target” effects can scuttle a promising drug. And the recent long-awaited presentation of results of a trial in which ezetimibe was added to moderate-intensity statin therapy in high-risk patients showed only modest benefit, though with excellent safety.