Good morning and welcome to the Enanta Pharmaceuticals conference call. At this time, all participants are on a listen-only mode. There'll be a question-and-answer session at the end of the prepared remarks. Please be advised this call is being recorded. I would now like to hand the call over to Jennifer Viera, Head of Investor Relations. Please go ahead.
Thank you, Operator, and thanks for joining us today. Announcing the results of RSVP, our phase II study of infants and children with RSV infection was issued this morning and can be found on the investor section of our website. Today's conference call is being webcast with slides. A copy of the slides will be posted on the events and presentations section of our website following the conclusion of today's conference call.
Participating on the call today is Dr. Jay Luly, President and Chief Executive Officer, and Dr. Scott Rottinghaus, Chief Medical Officer. Dr. Tara Kieffer, Chief Product Strategy Officer, and Dr. John DeVincenzo, Vice President of Translational Virology, will participate in the Q&A section. Dr. Luly will begin with opening remarks, followed by Dr. Rottinghaus, who will present the study results. After our formal remarks, we will open the call for Q&A.
Before we begin with our formal remarks, we want to remind you that we will be making forward-looking statements. These statements may include our plans and expectations with respect to the development and advancement of our RSV program, our research and development pipeline, and financial projections.
All of these statements involve certain assumptions and risks beyond our control that could cause our actual developments and results to differ materially from the statements. A description of these risks is in our most recent Form 10-K and other periodic reports filed with the SEC. Enanta does not undertake any obligation to update any forward-looking statements made during this call. I'd now like to turn the call over to Dr. Jay Luly, President and CEO. Jay?
Thank you, Jennifer, and good morning, everyone. I'm pleased to be with you this morning to detail the positive top-line results announced today from RSVP's, our phase II first in pediatrics study evaluating Zelicapavir as a treatment for respiratory syncytial virus, or RSV. At Enanta, we are committed to developing safe and effective RSV treatments to address the significant unmet need in high-risk patient populations where no RSV therapy exists today.
The data we'll present this morning from our first in pediatrics study of Zelicapavir represent a culmination of our efforts over many years to discover and develop effective RSV antivirals. This is a clear example of an RSV antiviral with positive data in a challenge study successfully translating into an antiviral effect in a real-world population with community-acquired RSV infection. We are excited to discuss these results and look forward to continued progress on our leading RSV portfolio.
Before we begin, I'd like to take a moment to thank all the patients and caregivers who participated in the study and our employees for their hard work and continuing contributions to our RSV programs. These results would not have been possible without their many contributions.
Dr. Scott Rottinghaus will go through the data in more detail momentarily, but I want to take this opportunity to highlight a few key points of this study. We were delighted to see not only an antiviral effect on our primary endpoint as well as secondary endpoints in the overall population, but the meaningful viral load decline of 1.4 log at the end of treatment in part two of the study, which was focused on virology.
Additionally, as this study was designed to understand the benefits Zelicapavir could provide in specific populations, we were also very encouraged to see similarly robust effects in a pre-specified subset of patients who entered the study within three days of having symptoms. We were also pleased to see a trend toward greater symptom reduction using our novel Resolve P tool in a smaller subset of patients.
Resolve P is specifically designed to assess the severity of pediatric RSV infection change over time based on observations by the child's caregiver and was developed in alignment with regulatory agency advice. We are currently in the process of validating this tool for use as an endpoint in a pivotal trial in alignment with regulatory agencies.
Furthermore, as the safety and tolerability demonstrated in this study is of utmost importance given the pediatric population, we are pleased to see a favorable profile consistent with prior clinical studies of Zelicapavir. We believe the totality of these data support further clinical evaluation of Zelicapavir in these pediatric patients who have a significant unmet medical need. I'll now turn the call over to Dr. Scott Rottinghaus to go through the data. Scott.
Thank you, Jay, and thanks to everyone for joining this morning's call. I'm very happy to share with you the data from our phase II pediatric study of Zelicapavir. Let's start here on slide seven with the study design and objectives. As a reminder, this was a double-blinded, placebo-controlled, randomized study aiming to enroll 88 children in two age cohorts.
The younger group was aged 28 days to six months, and the older group was six months to three years. Patients were given either Zelicapavir or placebo once daily for five days. Since this is the first time we studied Zelicapavir in infants and children, we did the study in two parts. First, we needed to determine the optimal dose for each age group. So part one focused on safety and pharmacokinetics for dose finding and was randomized two to one.
Patients in part one had to be enrolled within seven days of the onset of RSV symptoms. We then took the selected doses from part one forward into part two, where the primary objective was virology. Part two was randomized four to one. Because we were trying to see an antiviral signal in part two, we tightened the symptom window to five days for this virology-focused portion of the study.
We also looked at virology and other clinical endpoints across the entire study population. To review, then, the orange box at the right side of the slide shows the primary objectives of the study: antiviral activity in the overall population, safety and PK in the part one dose-finding portion of the study, and antiviral activity in the part two virology-focused portion of the study.
As a reminder, this study wasn't powered for statistical significance but was designed as a signal-finding study in different pediatric populations to inform a potential registration-enabling trial. We enrolled a broad pediatric population, including hospitalized patients as well as outpatients, aged 28 days to three years. We also pre-specified an analysis population of patients who were randomized within three days of symptom onset. Here's a summary of the results of the study.
Starting with safety, Zelicapavir was well tolerated with a favorable safety profile. No adverse events led to treatment discontinuation or study withdrawal. We saw an antiviral effect on the primary and secondary virology endpoints in the overall population, with a more pronounced antiviral effect observed in the pre-specified subset of patients who were randomized within three days of symptom onset.
Specifically, these patients had a viral load decrease of 0.9 log at day three and 1.2 log at day five as compared to placebo. Now let's get into the details of the study results. Slide nine shows the disposition of patients in the study. 99 patients were randomized, and 96 patients were dosed with either Zelicapavir or placebo. As you can see, there were 52 patients in part one and 44 in part two.
The efficacy population included 69 patients on Zelicapavir compared to 27 in the placebo group. All patients completed the study except for three who discontinued early for personal reasons. Baseline characteristics of the study were generally balanced across treatment groups. Patients were about seven months old on average. There was a slight imbalance on race, with more white children on Zelicapavir than on placebo.
Mean viral load at baseline was above six logs in both groups, and patients were randomized an average of four days after symptom onset. The majority of patients were hospitalized at baseline. In this study, Zelicapavir showed a consistent favorable safety profile. Adverse events were similar between Zelicapavir and placebo, with no adverse events leading to treatment discontinuation or study withdrawal.
Treatment-emergent adverse events occurred in 40% of the Zelicapavir patients and 50% of the placebo patients. Six patients on Zelicapavir had drug-related adverse events, all of which were mild or moderate in severity. Four of these patients had diarrhea, one had a skin rash, and one had a skin rash with leukocyte and neutrophil counts increased. Grade three adverse events were balanced between groups and not related to study drug.
One serious adverse event was observed in a patient dosed with Zelicapavir, a case of community-acquired pneumonia that began 17 days after the end of treatment. It was not considered to be related to study drug. This slide shows adverse events that occurred in more than one patient in any group. The most common adverse events in the Zelicapavir group were diarrhea and rash.
Other adverse events occurring in more than one patient on Zelicapavir were otitis media, eczema, and thrombocytosis, which is an increased platelet count that can be seen with RSV infection. Now turning to the PK results. Our goal in this study was to achieve similar drug exposures in children to exposure levels that were shown to be efficacious in the adult challenge study. Results showed that these target drug exposures were achieved across all age groups and dosing cohorts in both parts of the study.
We started at a dose of 5 milligrams per kilogram in all age groups, which was the final dose selected for children aged 28 days to 12 months. The dose was escalated to 7.5 milligrams per kilogram for children aged 12 to 36 months, and this was selected as the final dose for this age group. With both doses, all patients had model-predicted exposures above the efficacy threshold that was determined from the phase II challenge study.
Since exposure was similar across cohorts and all patients received a therapeutic dose, we pooled the patients from part one and part two for the primary efficacy analyses. Now let's turn to virology, the primary endpoint of the study overall. This slide shows the change from baseline in viral load as measured by PCR in the overall pooled efficacy population from both parts one and two of the study.
As you can see, there's a trend toward a greater viral load decline in patients treated with Zelicapavir compared to placebo, with the greatest difference at 0.7 log at day nine. Slide 15 shows the decrease in viral load, the primary endpoint for patients in part two of the study. Recall that this part had a shorter treatment window for enrollment and used the selected dose from part one, enabling this portion of the study to primarily focus on virology.
Here we see that Zelicapavir treatment resulted in a rapid and robust decline in viral load compared to placebo, with a one log drop as early as 48 hours after the initiation of treatment. This expanded to a 1.4 log drop at the end of treatment at day five.
The next slide shows the change from baseline in viral load in patients who were randomized within three days of symptom onset. This pre-specified analysis population, designated as the MITT3 population, includes about 40% of the patients in the study. As you can see here again, Zelicapavir treatment resulted in a substantial antiviral effect, with a viral load decline of about 0.9 log at day three and 1.2 log at day five as compared to placebo.
These data illustrate what we already know about respiratory infections, that treating earlier in the course of illness is important. These data also shed some light on what might be an appropriate treatment window for RSV. Moving to secondary endpoints, here we're showing the proportion of patients with undetectable RSV viral load over time.
In both the overall population and the patients randomized within three days of symptom onset, a greater proportion of patients on Zelicapavir had undetectable RSV RNA at days five and nine compared to placebo. Specifically, if you look at the MITT3 population, by the end of treatment at day five, about 17% of Zelicapavir patients were undetectable as compared to none on placebo. This effect persisted through day nine.
The next figure shows a Kaplan-Meier analysis of time to undetectable viral load. As you can see, Zelicapavir showed a qualitative improvement in time to undetectable viral load at early time points, although median time to undetectable viral load was similar between groups. In summary, for the virology data, we saw an antiviral effect for the primary and secondary virology endpoints in the overall population with once-daily dosing.
In part two of the study, which was the part focused on virology, there was a viral load decline of one log at day three and 1.4 logs at day five as compared to placebo. In the pre-specified analysis set of patients who were randomized within three days of symptom onset, a rapid and robust virology effect was observed. This subset represents 40% of the entire study population.
This three-day group of patients experienced a viral load decline of 0.9 log at day three and 1.2 log at day five compared to placebo. Secondary endpoints also supported the antiviral effects that we observed on the primary endpoints. A greater proportion of patients had undetectable viral load at days five and nine compared to placebo. We saw a qualitative improvement in time to undetectable viral load at early time points, although median time was similar between groups.
Finally, we saw an improvement in AUC of change from baseline for viral load at all time points. Importantly, these results were similar regardless of age or whether patients were hospitalized or outpatients. In this first in ped study, our goal was to gather preliminary information on RSV signs and symptoms as an exploratory endpoint. Because there was no validated symptom tool approved by regulatory agencies available, we've been developing our own proprietary tool in alignment with regulatory agency input.
This tool, called ResolveP, is a scoring system specifically designed to assess the change over time in severity of pediatric RSV infection based on observations by the child's caregiver. We developed this tool with input from caregivers, medical professionals, and regulatory agencies, and are currently conducting an observational study in pediatric RSV patients to generate quantitative evidence on the reliability, validity, and responsiveness of ResolveP in pediatric RSV.
As the tool was finalized and introduced late in the trial, data are only available from a small number of patients. Because our tool was not available at the beginning of the trial, we also included a publicly available tool called ReSViNET. This tool was primarily designed for prophylaxis studies to assess disease severity at a single time point. It was included as an exploratory endpoint at the start of the trial, so data are available for all patients.
As this trial was designed as a small signal-finding study, it was not powered to see an effect on symptoms. Using the ReSViNET tool, no difference in symptoms between treatment arms was observed. However, we were encouraged to see that ResolveP did show a trend toward greater symptom reduction with Zelicapavir in the small data set of 15 patients where results are available.
We plan to continue using our ResolveP going forward and are in the process of validating the tool for use as an endpoint in a pivotal trial. In summary, this study demonstrated that Zelicapavir was well tolerated with a favorable safety profile in children. There were no adverse events leading to treatment discontinuation or study withdrawal.
An antiviral effect was observed for the primary and secondary virology endpoints in the overall population, with a more pronounced antiviral effect observed in the pre-specified subset of patients randomized within three days of symptom onset. These patients had a viral load decline of 0.9 logs at day three and 1.2 logs at day five as compared to placebo. In conclusion, there's a substantial need for a safe and effective once-daily oral treatment for RSV, and we believe that the totality of these data support further clinical evaluation of Zelicapavir in children.
I'll now turn the call back to Jay.
Thank you, Scott. This study successfully confirmed a favorable safety profile for Zelicapavir, selected doses for pediatric patients, demonstrated a strong antiviral effect, and showed a trend in symptoms. We believe these data provide direction for a registration-enabling study and look forward to the continued development of Zelicapavir as we are excited about the potential to fill an unmet medical need in this vulnerable population.
In addition, results from RSV-HR, our phase II study in high-risk adults, will provide further insight into Zelicapavir's potential in another high-risk population. We expect to complete enrollment of this study during the current northern hemisphere RSV season. The phase II Zelicapavir data reported today come shortly after our positive results from a phase IIa human challenge study of EDP-323, our potent oral L inhibitor.
With positive results from both Zelicapavir and EDP-323, we continue to have the leading portfolio of RSV therapeutics with broad optionality, including a potential first-in-disease and best-in-disease compound. Furthermore, these distinct mechanisms have the potential to be developed as once-daily single agents or in combination for specific populations. This optionality provides us with multiple avenues to address different patient populations.
This is a pivotal time for us at Enanta as we enable both molecules to advance to the next stage of clinical development and evaluate potential paths for moving forward, including partnerships, with the singular goal of efficiently delivering transformative medicines to vulnerable patients suffering from RSV. I'll now turn the call back to the operator.
Thank you, ladies and gentlemen. If you have a question or a comment at this time, please press star 11 on your telephone.
If your question has been answered and you wish to move yourself from the queue, please press star 11 again. We'll pause for a moment while we compile our Q&A roster. Our first question comes from Roanna Ruiz with Leerink Partners. Your line is open.
Hey, morning, everyone. So a couple of questions for me. As a start-off, given the results today, how should we think about the potential primary efficacy endpoints that you could use in phase III for Zelicapavir? And are you planning to focus on virology only, or would you be able to validate the ResolveP tool and use it in phase III by that time?
Hi, Roanna. This is Scott. Certainly, for phase III, we're going to need clinical endpoints, and I think that symptoms are the most straightforward way to go. And we're very excited about our ResolveP tool.
We're actually working on validating that further. At present, we have a 100-patient observational study that's currently enrolling this fall, and we're very interested in moving that forward for a phase III endpoint. There's a variety of other things we could look at, but we think that symptoms are probably the most powerful for phase III.
Makes sense. And then a quick follow-up. I was curious, are you planning to focus more on hospitalized pediatric patients going forward, or would you still consider a mix of inpatient and outpatient?
Yeah, we're still looking at both at present. As I mentioned, about 80% of the patients in this study were hospitalized, but we saw similar good results in the hospitalized patients as well as the outpatients in this study. And so we think that both are really potential patient populations going forward.
Interesting. And last one for me.
Just was thinking about future utility and in a larger trial, would you consider enrolling patients who had previously received nirsevimab but possibly have breakthrough infections, maybe to just broaden the population eligible for Zelicapavir?
Yeah, absolutely. We think that RSV disease in patients who have severe enough disease to be clinically relevant in those patients who've been prophylaxed would still be a good target for use of a direct-acting antiviral like Zelicapavir. So we'd certainly be interested in further evaluating those patients.
Super helpful. Thanks.
One moment for our next question. Our next question comes from Akash Tewari with Jefferies. Your line is open.
Hi, this is Kathy on for Akash. So we saw that viral log at day five had a greater benefit in the overall population compared to the subgroup of patients with less than three days of symptom onset.
Were there any outliers in the overall population to cause this trend?
Oh, I think I see what you mean. I mean, certainly, there was some variability, as you might expect, among patients in the study. We just asked the parents of the patients how long their symptoms were, so there is some recall variability there. But overall, kind of as I mentioned in the presentation in the graphs, the patients who seem to have the greatest effect were the patients who were treated for smaller intervals after their onset of symptoms, if that makes sense.
Okay, great. Thank you. And then additionally, we saw that since Zelicapavir failed to show a symptom benefit with ReSViNET but showed a slight trend with ResolveP. Do you think this was a function of powering or effect size?
And then how might you be able to enhance for this moving forward to a phase III?
Yeah, I think it's a function of powering and the instrument used. I think it's important to have a validated instrument, and we're very excited, as I've mentioned, about ResolveP and the good results that we saw in the small patient population there. And I just think that we're going to need to actually power a study to find a symptomatic benefit. Once again, this was a PK and virology study, and we were actually pleased with the results that we were able to show as far as there were on symptoms.
Okay, great. Thank you so much.
Thank you, Kathy.
One moment for our next question. Our next question comes from Jay Olson with Oppenheimer. Your line is open.
Oh, hey, congrats on these results, and thanks for taking our questions.
Can you just talk about how these results, especially the 1.4 log viral load reduction, compare to what you were expecting from the study and anything that you found especially surprising in this data?
Yeah, we were actually really pleased with the magnitude of reduction. If you look at the 1.4 log reduction that we saw, it compares favorably with others. I'm sure you've noticed that ArcBio in their phase III showed a 0.6 log reduction at the equivalent of our day five. So our 1.4 and 1.2 in different data sets look good compared to that. Similarly, Rilumatavir in their three-day population showed about a 0.6 log reduction. So again, we're about double that. So as I say, this magnitude is pretty substantial compared to fusion inhibitors that have been in development.
Okay, great. Thank you. That's helpful.
Then can you just talk about the ReSViNET and ResolveP components and if there were any particular areas within those instruments where you saw especially promising results?
Yeah, so just to be specific, ReSViNET measures a whole variety of things kind of beyond what caregivers normally report. But to be specific, it looks at feeding intolerance, medical interventions, respiratory difficulty, respiratory frequency, apnea, general condition, and fever. Our ResolveP is a little bit different. It's very focused on things that caregivers can consistently measure and obviously an instrument that can be validated.
So ResolveP looks at difficulty breathing, wheezing, cough, stuffy nose, runny nose, sneezing, fever, appetite, activity, alertness and responsiveness, and crying. So the instruments overlap to some degree in their ability to measure the disease characteristics, but we think, once again, the ResolveP is probably a better measurement of symptoms over time.
And again, the sample was small, but we think that the results are promising.
Great. Thank you so much.
Thank you, Jay.
One moment for our next question. Our next question comes from Brian Skorney with Baird. Your line is open.
Hey, good morning, everyone. Thanks for taking my question. So just given this result and some of the color around sort of the potential clinical benefit around ResolveP, how do you think about going about powering a phase III program? Do you really need to look more at sort of the natural history of ResolveP to try to figure it out? It just seems like it'd be hard to kind of think about powering specifically around clinical endpoints versus virology at this point.
Sure, Brian. So we're working on that right now. As I mentioned, we have a natural history study in progress.
You can see a treatment effect here, but I think we need to do a little bit more comparison and figure out really the magnitude of the treatment effect for powering a pivotal trial.
Great. Thanks.
One moment for our next question. Our next question comes from Ronan with J.P. Morgan. Your line is open.
Hi guys, this is Ronan for Eric. First question, what would be a meaningful effect size in either of the available symptom scales you used if one is ultimately advanced to a pivotal study? And is time to resolution of particular symptoms an endpoint that was considered? And what might be a compelling difference here? Thanks.
Hey, Ron, it's Scott. Could you repeat the first half of your question again? You were talking a little fast, and I couldn't make it all out. Sure.
What would be a meaningful effect size in either of the available symptom scales if one is eventually advanced to that pivotal?
All right. So Ron, kind of as I was alluding to, we're trying to work out in our validation process what the clinically meaningful effect size is, and we don't have that fully established yet. So still to come. And then what was the other half of your question?
Is it time to resolution of any particular symptom and endpoint that was considered? And what would be the difference here?
Oh, yeah. So I guess for some contextualization, I'm sure you know that Oseltamivir was shown to reduce symptoms by one day in influenza. Certainly, we would hope to do at least that well. And obviously, we're continuing to develop our ResolveP and figure out what we can do.
Okay. And then just one more.
How are you thinking about any potential read-through from this study into the high-risk patient population? Anything you would be changing in your exploratory endpoints, specifically in regards to the symptom rating scales? So can you repeat the first few words? Did you say read-through? Yeah, any read-through from this study to the high-risk patient population.
Oh, yeah, so this certainly encouraged us, Ronan. It's great to have this proof of concept in a real patient population. This is a really strong translation of our challenge study results into a natural or real-world patient population showing that we can really see the antiviral effect, so we're very encouraged about what we might be able to see in the adult high-risk study as a result, and as we've said, we're enrolling that study fairly nicely and hope to complete it later this season.
I would also point out that the adult high-risk study has a three-day treatment window as a maximum, and it's also a larger population, about 180 people with a clinical endpoint. So we think that should really be able to add a lot of data to our knowledge.
Thank you so much.
Thanks, Ron.
One moment for our next question. Our next question comes from Roy Buchanan with Citizens JMP. Your line is open.
Hey, thanks for taking the question. I guess to follow up on the last set, for the RSV HR, can you just detail what the symptom score is and who's making that evaluation? Is there any potential for a physician-made evaluation?
Yeah, so it's a score called the RIIQ. And once again, it's a symptom score. The principal investigator actually makes the calls on those, and it's done in a blinded fashion, obviously.
RIIQ is a score that's used for adults. It's totally different than the pediatric scores that are used in this study, but measuring symptoms as well.
Okay, got it. And then just a couple of the observational study, what ages are being included in that study? And then back to RSVPs, are you going to follow up the viral load results with a cell culture-based assessment like a POC assay or something? Thanks.
Yes, thanks, Roy. In terms of the observational study, it has the same age groups as are studied in this pediatric study. It's 28 days up to 36 months. And then in terms of culture, yes, absolutely. We do have culture results. They're supportive of these results as well, and we'll be presenting those at a medical meeting soon.
Thank you.
One moment for our next question.
Our next question comes from Ed Arce with H.C. Wainwright & Co. Your line is open.
Hi, congrats on the data, and thanks for taking my questions. First, I wanted to ask one of the previous questions around the differential between the day five antiviral response between the overall study and those that were randomized within three days.
Just wondering if you could discuss the assumptions around the optimal window of that randomization. And given that there's this variability with caregivers recording the time of treatment onset, is there anything perhaps that you learned in this trial that you could use to improve that variability in the next trial? Thanks.
Oh, excellent question. So as a general principle, as we expected and as has been seen with other antivirals, a shorter window of symptoms to treatment is, in general, better than longer.
And we looked at the day five results and didn't see as good of an effect as the day three. So certainly, shorter is better, and whether that's day three, day four, whatnot, we need to determine. The second half of your question, I'm trying to remember. Oh, the variability.
Yeah. So we need to look at that. I mean, it's sometimes a little bit difficult for parents to remember, right? They're a little bit flustered coming into the hospital, and we ask, "How long did your baby have symptoms?" And it depends on how closely they're looking. And we'll obviously just have to work on what we can do, but there is some recall bias involved, and that's essentially been seen in all studies.
Okay. Next question, just around the end of the study data. At day 14, the overall placebo viral load was a bit lower than Zelicapavir.
I'm just wondering how we should think about that, how that translates perhaps into the next studies.
Yeah. So there are a few things to be considered. So first of all, pediatric patients on their first episode of RSV infection have been shown in natural history studies to have detectable viral loads out to 30 days. So it's no surprise that we're seeing substantial detectability in both groups at day 14. The other issue is that down around the limits of detection, right?
These are very low viral loads. So you can see a lot of variability in terms of what's detectable and what's not. So again, no great surprise there. The third issue is that this is a treatment study of five days, and now you're looking out at day 14. And then the final issue is it's just variability in a relatively small patient population, right?
This is a study of 96 kids with a fairly small number of placebos. So there's just some variability out there that I think can account for what we saw at day 14.
Right. Okay. And then just thinking through to the next steps, obviously this data focused on the virology, but you mentioned your intent to focus phase III on clinical endpoints and perhaps look to use the ResolveP symptom tool that you've developed. I'm wondering how you would translate the virology to the symptoms and if virology would indeed be necessary for a registrational enabling study.
Yeah. My expectation is that virology would not be necessary. Regulators approve drugs on clinically meaningful endpoints, and that is kind of the key, as you noted, Ed. We're going to have to do something clinical, and I think the answer is probably symptoms. Okay.
Then last question, just on next steps, is there anything you could share with us in terms of timelines, perhaps meeting with the FDA, other gating steps before you're ready to move forward?
Hi, Ed. This is Jay. We will be scheduling meetings here with FDA for obviously, it'll be next year. But we're moving the program forward in terms of enablement for registration study, as well as, as I mentioned, EDP-323. We have. You saw that really nice challenge study data that we generated on that, which is probably the best challenge study data that we've ever seen.
We're still sort of gearing both assets up for progression. One, again, moving forward toward a phase 3. The other, moving forward toward a similar type of study as the pediatric study so that these could be enabled basically a year from now to move forward.
And so we'll figure out that exact path for each of them. And as I mentioned in my remarks, up to and including the possibility of a partnership.
Right. That's very helpful. Thanks, Jay and Scott.
Thank you, Ed.
One moment for our next question. Our next question comes from Liisa Bayko with Evercore ISI. Your line is open.
Hi there. Thanks for taking the question. Just a couple for me. Did you see any difference in hospitalization or kind of, I guess, getting out of the hospital faster or anything along those lines?
Yeah. So Liisa, we actually didn't see a difference in time to hospital discharge. Again, not a big surprise in this size of study. Time to hospital discharge is kind of variable and subjective depending often on social issues of when the parents are comfortable taking the patient home. So didn't see a difference there.
Okay.
That's helpful. Thanks. And can you talk about the difference between the PRO you're trying to validate and ReSViNET and ResolveP? Just curious on kind of why you were starting to see some trends in that, but not the others. What are some of the key differences?
Yeah. So I think the fundamental difference, and I kind of went over the specific components earlier, but I think the most fundamental difference is that the ReSViNET instrument was never designed to look at change over time. It's a rating scale to see how sick a kid is at a point in time, and it was designed for entering kids into studies and basically stratifying them to one group or another, but not as an endpoint to look at change.
In contrast, ResolveP is in the process of being validated to do that very thing, to be a study endpoint to look at how kids are changing over time. So I think that that's the key benefit of ResolveP versus ReSViNET. And obviously, we're still working on fully validating that instrument, but we feel we're making good progress, and we've received good regulatory feedback on that instrument.
Okay. And with respect to validating the ResolveP tool, could you maybe speak to a little bit more about when we're going to have data and what you're starting to see in terms of what would be a clinically meaningful threshold and how that relates to sort of the initial data in the 15 patients you just saw? I mean, is that kind of in the range of what would be clinically meaningful? Do you have a sense yet?
I know you're still in the process. Give us a sense. Oh, yeah. Thanks, Lisa. So I think it's hard to tell, again, based on a small sample size here in phase two, but what we're seeing is promising. And kind of as I alluded to, over time, we've worked on validating the tool with caregivers and medical providers and gotten regulatory feedback and worked with expert PRO developers to make sure that this tool is as optimized as possible.
So as I mentioned, we have an observational study ongoing, and we expect that finally our next study would provide the final data that we need to really fully validate the tool for broad use as an endpoint. Okay. So sort of timing on the validation then, when we would know what the clinically meaningful threshold, when would that be? I don't have a specific answer for you, Lisa.
It's being worked up. And as you may know, the final validation is always done with a relatively larger clinical trial to figure out what the threshold would be.
Okay. But you'd have to have that, would you have to have that done prior to phase three or at least have some sense of what? Or how does it work?
Yeah. Not necessarily. So you can use a non-fully validated tool in a phase three. And obviously, in a phase three, we would do an interim analysis to look at the treatment effect and make sure things are on track in terms of study powering so that we don't, so that we don't make a mistake and power a study too small or too larg e.
Yeah. I guess it's hard now because you don't have a sense of what the target is.
So how do you power the study in that way, I guess? It's a little bit of a challenge. Is that correct?
Yeah. I mean, once again, we're continuing to work on it both through observational studies. And here we have a small treatment effect.
Okay. And can you tell us what the P value was just for the antiviral effect?
Yeah. So the antiviral effects were qualitatively good, and you saw the point estimate, but they don't have statistically significant P values. Again, the study is not designed in order to show that.
Okay. And then just final question. You did have an imbalance in ethnicity. Maybe a question for Dr. DeVincenzo. Is there any kind of, I guess, background or understanding? Are there differences across ethnicities in terms of response to RSV, kind of natural immunity, and how that antiviral effect may change across ethnicities?
Just wondering if that was an influencing effect at all. Thanks.
Yeah. There really is. I mean, RSV is kind of an equal opportunity offender, and it's surprising that there really isn't that much difference between racial distributions about natural history of RSV viral load and how quickly they get rid of it. It's age-dependent a little bit, and it's certainly consistent with the data that we've seen here, and within our study, there didn't appear to be any ethnic/racial differences.
Okay. Great. Thank you so much.
Thanks, Lisa.
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