Enanta Pharmaceuticals, Inc H.C. Wainwright 28th Annual Global Investment Conference

Sure. Before I begin, I want to remind you that I will be making some forward-looking statements. For a summary of the risks associated with these statements, please see our filings on sec.gov and on our website. The last 12 months, I think one of the things that the 12 months have given us is a real insight into how to treat high-risk RSV patients. So we had a data set that set the stage for what is now a registration study for zelicapavir, our lead RSV asset. The other is it has allowed us a chance to sort of spread our wings and grow beyond just virology in the I&I space.

To that end, we've brought forward a KIT inhibitor into the clinic, a STAT6 development candidate, and a new program that's also going after mast cells as KIT is MRGPRX2, and setting the stage for the next 12 months of having data sets starting to read out in multiple of those.

Well, one thing, again, there are no approved RSV treatments. Prophylaxis, after 70 years, has started to come onto the scene, but treatments are still unavailable for patients. One of the things that we wanted to sort out is really trying to figure out what is the path to registration, since no one's ever done it before. To that end, we had an end-of-phase II meeting with the agency and really sat down to design what is the trial design, the path, registration endpoints, patient populations, et cetera. Where we landed was the good news is we didn't need to do two phase IIIs. FDA said as long as we had this supportive lead-in phase IIb study to the phase III, it could be a single phase III. That was good. We aligned on the HR3 patient population as being a good one to test.

That was the patient population where we saw a signal in our prior high-risk adult study, where we saw that patients 75 and older or who had COPD or who had congestive heart failure, those three patient populations, if you will, and some had multiple of them, were in a position to give us a strong signal. We saw that. So we agreed on the patient population and also the endpoint, the time to complete resolution of symptoms. We also saw an effect on hospitalization, so that was good. We're looking at that as a key secondary endpoint. It was overall clarifying, and it gives us a clear look in terms of how to progress this.

Well, when we went into the prior study, it was a little more of a broad survey in terms of different patient populations. In fact, we had people who were 65 and older in there. We also had the 65 to 74 group in there. We had asthmatics in there in the prior study. What we did in the first study was we capped the numbers of asthmatics and people who were 65 to 74 and otherwise healthy because we didn't want otherwise healthy, mild, 28-year-old asthmatics dragging down the signal that we might see in true high-risk patients. That was a teaching from the first study that we learned because we had it pre-specified to maximize or, I'm sorry, to cap at 20% those asthmatics in the 65 to 74-year-olds so that 80% would be that HR3, and that's exactly what we saw.

That was one of the teachings that we carried into the new study. We're only looking at the HR3 population. Also the time to complete resolution. We found that that was the readout that gave the strong signal in that patient population. So we changed the primary endpoint of the study once we saw where the real signal was.

Yeah. The phase II-B is really just to kind of confirm the elements now that we sort of focused on "the right high readout patient population," the endpoint with the large signal. It is basically a recapitulation in a certain way to make sure we can confirm that and also to look at the effect size to make sure we do not need to tweak a sizing element in the phase III component, either up a little bit or down a little bit, depending upon the signal. I think that is basically it. It should be hopefully pretty streamlined.