An Interventional Decentralized Phase 2, Randomized, Double-Blind, 2-Arm Study to Investigate the Efficacy and Safety of Orally Administered Nirmatrelvir/Ritonavir Compared with Placebo/Ritonavir in Participants with Long COVID

This decentralized trial is a Phase 2, 1:1 randomized, double-blind, superiority, placebo-controlled study in an anticipated 100 non-hospitalized highly symptomatic adult participants with long COVID. It seeks to determine the efficacy, safety, and tolerability of 15 days of Paxlovid (nirmatrelvir/ritonavir), an anti-viral agent, compared with placebo plus ritonavir. The hypothesis is that viral persistence contributes to long COVID in some patients and nirmatrelvir/ritonavir compared with placebo/ritonavir can improve general health status in participants with long COVID. The study will also seek immune signatures associated with treatment response (overseen by Professor Akiko Iwasaki).
The decentralized study does not require site visits, and participants in all 48 states including the District of Columbia, who meet entry criteria can enroll. It is designed to make it convenient to participate. The study drugs will be delivered to the participant's designated address.
Long COVID is also known as post-acute sequelae of SARS-CoV-2 (PASC).

Start Date14 Apr 2023

Sponsor / Collaborator

Yale University

[+1]

NCT05545319

/ WithdrawnPhase 2

AN INTERVENTIONAL EFFICACY AND SAFETY, PHASE 2, DOUBLE-BLIND, 2-ARM STUDY TO INVESTIGATE ORALLY ADMINISTERED NIRMATRELVIR/RITONAVIR COMPARED WITH PLACEBO/RITONAVIR FOR THE TREATMENT OF SEVERE COVID-19 IN HOSPITALIZED PARTICIPANTS WHO ARE IMMUNOCOMPROMISED OR AT INCREASED RISK FOR SEVERE COVID-19 OUTCOMES

A Study to Learn About the Medicine Called Nirmatrelvir Used in Combination With Ritonavir in People with Weakened Immune Systems or at Increased Risk for Poor Outcomes who are Hospitalized Due to Severe COVID-19

Start Date13 Dec 2022

Sponsor / Collaborator

Pfizer Inc.

NCT05441215

/ CompletedPhase 1

A PHASE I, MULTIPLE DOSE, OPEN-LABEL PHARMACOKINETIC STUDY OF NIRMATRELVIR/RITONAVIR IN HEALTHY LACTATING WOMEN

The main purpose of this study is to measure the level of active ingredient of the study medicine (nirmatrelvir) that is secreted in human breast milk when it is given to healthy breastfeeding women. The study medicine consists of two medicines, nirmatrelvir and ritonavir. We are seeking female participants who are:
Actively breast-feeding (lactating) at least 12 weeks postpartum;
Age between 18 to 55 years and not currently pregnant;
Have a Body Mass Index (BMI): 17.5 kg/m2; and a total body weight >50 kg (110 lb).
Participants will take the study medicine by mouth for a total of 3 times over 2 days (2 morning doses and 1 evening dose) at the study clinic. We will periodically collect breast milk from day 2 to 4 to measure the level of nirmatrelvir and ritonavir in it. A safety follow up call will be conducted around 28-35 days from the last dose to monitor any reactions participants may have to the study medicine.

Start Date12 Dec 2022

Sponsor / Collaborator

Pfizer Inc.

100 Clinical Results associated with Nirmatrelvir

100 Translational Medicine associated with Nirmatrelvir

100 Patents (Medical) associated with Nirmatrelvir

1,933

Literatures (Medical) associated with Nirmatrelvir

31 Dec 2025·Journal of Medical Economics

Cost-effectiveness of outpatient COVID-19 antiviral treatment with nirmatrelvir/ritonavir versus usual care in Swedish patients with various risk factors

Article

Author: Gerdesköld Rappe, Christian ; Nilsson, Fredrik ; Mugwagwa, Tendai ; Aldvén, Martina

AIMSNirmatrelvir/ritonavir (NMV/r) is an orally administered antiviral indicated for the outpatient treatment of adult patients with mild-to-moderate COVID-19 at high risk for disease progression to severe illness. We estimated the cost-effectiveness of NMV/r versus best supportive care for 54 patient cohorts, specified according to age, vaccination status and comorbidity burden.MATERIALS AND METHODSA previously published and validated cost-effectiveness model was utilized and adapted to the Swedish setting. The model used a short-term decision-tree (1 year) followed by a lifetime 2-state Markov model. The short-term decision-tree captured costs and outcomes associated with the primary infection. Post-acute COVID-19 syndrome was only considered in terms of quality-of-life decrements for one year. Baseline hospitalization and mortality risks were taken from a Swedish, nationwide, uniquely granular, Omicron-era, real-world study. NMV/r effectiveness were taken from an Omicron-era US real-world study. Remaining inputs were informed by previous COVID-19 studies and publicly available Swedish sources.RESULTSThe incremental cost-effectiveness ratios (ICERs) showed a large variation ranging from almost nine million SEK for some of the youngest cohorts to being dominant (i.e. cost-saving with higher gains in quality-of-life vs standard of care) for twelve elderly cohorts. In general, higher age in combination with non-recent (>180 days) or no vaccination led to lower ICERs. Specifically, NMV/r was cost-effective for all but one patient cohorts at least 70 years old, and for most patient cohorts 60-69 years old.LIMITATIONSAs the COVID-19 landscape changes, symptom burden and baseline risks constantly change. Thus, the cost-effectiveness of NMV/r will change with time. However, the future risks could be related to the risks in the current study, and thus remain useful for decision makers.CONCLUSIONSThis study shows that NMV/r is a cost-effective or even cost-saving treatment option for many patient cohorts, including most elderly and not-recently vaccinated patients with at least some comorbidity burden.

31 Dec 2025·Annals of Medicine

Early combination of sotrovimab with nirmatrelvir/ritonavir or remdesivir is associated with low rate of persisting SARS CoV-2 infection in immunocompromised outpatients with mild-to-moderate COVID-19: a prospective single-centre study

Article

Author: Buonomo, A. R. ; Moccia, M. ; Silvitelli, M. ; Trastulli, F. ; Gravetti, A. ; Scotto, R. ; Grimaldi, F. ; Cuccurullo, F. ; Gentile, I. ; Palmieri, S. ; Mercinelli, S. ; D’Agostino, A. ; Pietroluongo, D. ; Viceconte, G.

BACKGROUNDImmunocompromised patients are at high risk of developing persisting/prolonged COVID-19. Data on the early combined use of antivirals and monoclonal antibodies in this population are scarce.RESEARCH DESIGN AND METHODSWe performed an observational, prospective study, enrolling immunocompromised outpatients with mild-to-moderate COVID-19, treated with a combination of sotrovimab plus one antiviral (remdesivir or nirmatrelvir/ritonavir) within 7 days from symptom onset. Primary outcome was hospitalization within 30 days. Secondary outcomes were: needing for oxygen therapy; development of persistent infection; death within 60 days and reinfection or relapse within 90 days.RESULTSWe enrolled 52 patients. No patient was hospitalized within 30 days of disease onset, required oxygen administration, died within 60 days, or experienced a reinfection or clinical relapse within 90 days.The clearance rates were 67% and 97% on the 14th day after the end of therapy and at the end of the follow-up period, respectively.Factors associated with longer infection were initiation of therapy 3 days after symptom onset and enrollment for more than 180 days from the beginning of the study. However, only the latter factor was independently associated with a longer SARS-CoV-2 infection, suggesting a loss of efficacy of this strategy with the evolution of SARS-CoV-2 variants.CONCLUSIONSEarly administration of combination therapy with a direct antiviral and sotrovimab seems to be effective in preventing hospitalization, progression to severe COVID-19, and development of prolonged/persisting SARS-CoV-2 infection in immunocompromised patients.

31 Dec 2025·Emerging Microbes & Infections

Effectiveness of nirmatrelvir/ritonavir and molnupiravir on post-COVID-19 outcomes among outpatients: a target trial emulation investigation

Article

Author: Chong, Ka Chun ; Jiang, Xiaoting ; Guo, Zihao ; Chow, Tsz Yu ; Mok, Chris Ka Pun ; Wang, Huwen ; Jia, Katherine Min ; Yang, Aimin ; Li, Conglu ; Hui, David S. C. ; Li, Kehang ; Hung, Chi Tim ; Wei, Yuchen ; Wang, Yawen ; Zhao, Shi ; Boyer, Christopher ; Lin, Guozhang ; Yeoh, Eng Kiong ; Yam, Carrie Ho Kwan

Limited studies compared the effectiveness of nirmatrelvir/ritonavir and molnupiravir against a control group on post-COVID-19 conditions. Our study examined the association of nirmatrelvir/ritonavir and molnupiravir with post-acute mortality and hospitalizations among outpatients using real-world outpatient records of COVID-19 designated clinics in Hong Kong. This is an observational study using a target trial emulation framework, involving nirmatrelvir-ritonavir versus no antiviral treatment (Trial 1) and molnupiravir versus no antiviral treatment (Trial 2). Outcomes included post-acute mortality, all-cause hospitalization, and hospitalization due to 13 selected sequelae. Relative effectiveness was assessed by comparing the cumulative incidence between two groups, reported as relative risk (RR), along with risk differences (RD) during day 0-30, 31-180, and 181-360. After screening, 140,477 and 96,030 patients were included in Trial 1 and 2, respectively. Compared with no treatment, nirmatrelvir/ritonavir-treated patients exhibited a significantly lower risk of post-acute mortality (31-180 days: RR, 0.71; 95% CI, 0.54-0.96; RD, 0.20%; 181-360 days: RR, 0.64; 95% CI, 0.50-0.82; RD, 0.32%) and all-cause hospitalization (31-180 days: RR, 0.82; 95% CI, 0.76-0.88; RD, 1.11%; 181-360 days: RR, 0.83; 95% CI, 0.78-0.89; RD, 1.18%). Patients receiving molnupiravir had a lower risk of 30-day mortality, but no significant beneficial effect was observed for the post-acute outcomes. In conclusion, this study demonstrated the effectiveness of nirmatrelvir/ritonavir in reducing post-COVID-19 outcomes among outpatients. While we observed the short-term effectiveness of molnupiravir in reducing mortality, no protective effect on long-term post-COVID-19 outcomes was observed.

222

News (Medical) associated with Nirmatrelvir

28 Mar 2025

·endpts.com

‘People will die’: End of NIH grants guts work between academics and companies to counter next pandemic

On Tuesday, drug discoverer and biotech entrepreneur Alpha Lee told scientists at a chemistry meeting about a new molecule to combat the Zika virus. There are no treatments designed to stop the mosquito-borne infection, which can cause birth defects. After three years of work, Lee and a team of collaborators had made a compound that shut down an enzyme that’s essential for Zika virus replication. But his excitement was short-lived. After the conference session ended, Lee checked his email and saw that the $67 million federal funding supporting the work and several other antiviral programs had been terminated. “The end of the pandemic provides cause to terminate COVID-related grant funds. These grant funds were issued for a limited purpose: to ameliorate the effects of the pandemic. Now that the pandemic is over, the grant funds are no longer necessary,” said the email, which was reviewed by Endpoints News . Zika and Covid have nothing to do with one another. But Lee is one of more than a dozen researchers who told Endpoints that their funding from the National Institutes of Health was cut off as part of the Trump administration’s efforts to stop research on Covid-19 and the virus that causes it, SARS-CoV-2. Some of those researchers were finding ways to make vaccines that could induce sweeping protection against many kinds of coronaviruses. Others had similar efforts focused on antivirals. Yet in many cases, including Lee’s, the research went far beyond the recent pandemic and focused on ways to combat more than a dozen deadly viruses with pandemic potential, many of which have no good treatments. “This was never about Covid. This is about being prepared for the next viral pandemic, which is going to come, we all know it,” said Norbert Bischofberger, a former Gilead Sciences executive who served as an unpaid advisor to a group from the University of California, San Francisco, whose final two years of a $67 million grant were also cut off. While most of the terminated research was spearheaded by academic labs, several of them were working closely with drug companies on the programs. Lee is cofounder and chief scientific officer of a small biotech startup called PostEra. Other labs in the program were working with bigger pharma companies including Johnson & Johnson, Merck, Novartis and Roche. The cuts jeopardize the drugs they were working on, many of which would only become profitable during a pandemic. (While aspects of the research cuts have been reported earlier this week, Endpoints is the first to report their ties to industry drug development efforts.) “I don’t know what to do with these programs,” said Nevan Krogan, a biologist at UCSF whose funding to develop new antivirals was cut. “If these were cancer drugs, pharma would be all over this, because they can make money, right? But they can’t make money on this unless there’s a pandemic.” Lee and Krogan were both funded through a $577 million award from the National Institutes of Health in 2022 to establish nine Antiviral Drug Discovery (AViDD) centers across the country. The goal for each center was to work on at least one new drug to help protect against future coronavirus outbreaks and at least one drug targeting another viral family with pandemic potential. The nine AViDD centers have been even more productive than hoped. They’ve made leads on dozens of potential drugs against at least 18 viruses, including an enterovirus that some scientists have warned could become “airborne polio,” and the Middle East Respiratory Syndrome (MERS) coronavirus, which has a fatality rate of about 30%. “The goal is not just to create knowledge. The goal was to develop products that could really have an impact on protecting human health.” said David Perlin, chief scientific officer of the Hackensack Center for Discovery and Innovation in New Jersey, who co-led an AViDD center focused on making antivirals for several diseases transmitted by mosquitos, including chikungunya and yellow fever. Perlin’s group also worked with Merck on a pan-coronavirus pill that targeted the viral protease, the same target of Pfizer’s drug Paxlovid. The new compound could be an improvement because it doesn’t require the coadministration of an HIV antiviral called ritonavir used to prevent the rapid breakdown of the coronavirus-targeting portion of the drug, called nirmatrelvir. Ritonavir is responsible for some of Paxlovid’s side effects and its interactions with other drugs restricts the patients who can get it. More importantly, the new drug might protect against coronaviruses that have yet to cause a pandemic. Perlin said that it “would be valuable in the Strategic National Stockpile as a way to prevent what we saw with COVID-19, where we had essentially no countermeasures.” Three drug companies — Gilead, Merck and Pfizer — were only able to quickly develop antivirals for Covid during the pandemic because of earlier work on those molecules. When it became clear that the drugs might work against SARS-CoV-2, the companies dusted them off and quickly moved into clinical studies. But all three of those drugs were far from perfect and left room for improvements. Another two years of funding would have supported the preclinical safety studies needed to get the new pan-coronavirus inhibitor ready to test in humans, Perlin said. Merck didn’t respond to a request for comment about the drug’s future. Perlin described his AViDD center as a network of 200 people that formed “a real drug discovery enterprise for rapid response, no matter the threat.” But with the funding pulled, Perlin said that many of the scientists involved will have to find new jobs. Leaders from other AViDD centers also said they will have to make layoffs. “It clearly makes us more vulnerable,” Perlin said. “When you dismantle infrastructures, you have to reassemble them, and that takes time. That means your response to the next threat is just going to be that much slower and more difficult. And there will be casualties.” Funding for AViDD centers was originally supposed to run through April 2027. The future of the programs was already called into question once in late 2023 when the NIH, under the Biden administration, informed centers that the funding for the final two years was gone. Many centers began saving to focus on their best programs and access unspent money through the NIH’s no-cost extension procedure, allowing researchers to stretch out a grant’s timeline by dipping into unused funds. But now that money has been cut off as well. An NIH spokesperson did not respond to questions about why research grants on viruses beyond SARS-CoV-2 were included in the Covid cuts. But they shared a statement saying that the agency “is taking action to terminate research funding that is not aligned with NIH and HHS priorities.” At UCSF, Krogan’s AViDD center has also advanced inhibitors targeting four different coronavirus proteins into IND-enabling studies. One of its more exploratory efforts was focused on how to develop drugs that directly target viral RNA, instead of viral proteins. “If it works, it will have an impact on any RNA virus,” Krogan said. “They made a huge amount of progress,” said Bischofberger, who advised the group. “It’s not that industry couldn’t do this. But you can’t really justify spending public investors’ money on something that is hypothetical in the future,” Bischofberger added. “And startup companies will never get any funding for this kind of work, because venture capitalists will say where’s my return on investment and you may never get one.” Krogan said his group has been in close contact with Roche, which has an advisory role in the programs, but has not made any formal commitment to develop the drugs. A company spokesperson said that “Roche remains committed to advancing research and developing innovative antiviral medicines to address both current and emerging viral threats.” Other AViDD centers were also partnering with drug companies on a variety of antivirals. Johnson & Johnson was working with the University of North Carolina at Chapel Hill on drugs for flaviviruses like West Nile virus and dengue fever. The company, which downsized its infectious disease unit in 2023, did not respond to questions about the future of the programs. Novartis was working with The University of Texas Medical Branch (UTMB) on antivirals against flaviviruses, henipaviruses, and coronaviruses. UTMB researcher Vineet Menachery told Endpoints the group has stopped work on the projects due to funding cuts but “are hoping for reversal of this decision.” A Novartis spokesperson said the company remains “committed to our antiviral work and are evaluating options for the program.” With three separate coronavirus outbreaks this century, many scientists say a fourth is inevitable. One of the best ways to prepare is to make better vaccines. But Duan Wesemann, an immunologist at Mass General Brigham, told Endpoints that his $7.8 million grant that could help make vaccines with broader immunity was cut. “The rationale given was that ‘the pandemic is over,’ but the scientific questions are not,” Wesemann said in an email. “Terminating funding like this not only halts scientific progress—it potentially sets us back years in understanding how to design next-generation vaccines or predict immune durability.” Likewise, Theodora Hatziioannou, a scientist at Rockefeller University, was part of a team trying to develop a shot that could trigger broadly-neutralizing antibodies against coronaviruses yet unseen. Cutting this research now leaves the country, and the world, more vulnerable, Hatziioannou said, a fear echoed by several other researchers Endpoints interviewed. “People will be screwed,” Hatziioannou said. “You can cut all of this and the immediate effects will be negligible. The effects are going to appear in 5 to 10 years. People already forget what happened in the beginning of the Covid epidemic. The hospitals were full of people, trucks were carrying out bodies. This can happen again, and we will be less well prepared for it, and people will die.” Editor’s note: This article was updated to correct Alpha Lee’s title to chief scientific officer.

06 Mar 2025

·www.drugs.com

Paxlovid May Offer Little Benefit for Vaccinated Older Adults

THURSDAY, March 6, 2025 -- The antiviral drug Paxlovid may not offer much protection against COVID-related hospitalizations or deaths for vaccinated older adults after all. Research published recently in JAMA Network Open looked at data from more than 1.6 million adults ages 65 to 74 in Ontario, Canada, during 2022. Most participants (nearly 88%) had received at least two doses of the COVID vaccine, and only certain high-risk groups or adults 70 and older were eligible for Paxlovid at the time. The study found that Paxlovid did not significantly reduce the risk of hospitalization or death from COVID in this mostly vaccinated population. “We were surprised and disappointed,” lead study author John Mafi , an associate professor of medicine at the David Geffen School of Medicine at UCLA, told The Washington Post . “We concluded that it’s because it’s a highly vaccinated group with 88 percent fully vaccinated,” he added. The findings could help older adults weigh the benefits and costs of taking Paxlovid. “The cost is part of the calculus because it’s $1,650 per treatment course,” Mafi said. “I think that needs to be part of the conversation.” A spokesperson for Pfizer, which makes Paxlovid, said the company stands by its effectiveness for patients at high risk for severe illness. What's more, Paxlovid may still be helpful for certain high-risk groups, Mafi said. “If you’re immunosuppressed, if you have cancer , chemotherapy , if you are frail, if you’re living in a nursing home, if you have end-stage kidney disease, if you’re an organ transplant recipient, those are very high-risk conditions,” he told The Post . “I would be more cautious in those groups.” Paxlovid, a combination of nirmatrelvir and ritonavir, has been shown to reduce hospitalizations and deaths in unvaccinated, high-risk adults. But prior research found it didn’t significantly shorten COVID symptoms in vaccinated adults. At best, the drug lowered hospitalization risk by 1.3 percentage points in this new study. “If you are vaccinated without additional risk factors, I wouldn’t prescribe Paxlovid, and I probably wouldn’t take it if I was a patient,” study co-author Dr. Peter Wu , associate professor of medicine at the University of Toronto, told The Post . Whatever your topic of interest, subscribe to our newsletters to get the best of Drugs.com in your inbox.

VaccineClinical ResultmRNA

10 Feb 2025

·ir.enanta.com

Enanta Pharmaceuticals Reports Financial Results for its Fiscal First Quarter Ended December 31, 2024

On Track to Report Topline Results for RSVHR, a Phase 2 Study of Zelicapavir in High-Risk Adults Infected with Respiratory Syncytial Virus (RSV), in 3Q 2025 Advancing Immunology Portfolio with Ongoing IND Enabling Studies of KIT Inhibitor EPS-1421 On Track to Announce STAT6 Development Candidate in 2H 2025 Operations Supported by Cash and Marketable Securities Totaling $216.7 Million at December 31, 2024 , as well as Continuing Retained Royalties WATERTOWN, Mass. --(BUSINESS WIRE)--Feb. 10, 2025-- Enanta Pharmaceuticals, Inc. (NASDAQ:ENTA), a clinical-stage biotechnology company dedicated to creating small molecule drugs for virology and immunology indications, today reported financial results for its fiscal first quarter ended December 31, 2024 . “2025 is primed to be a pivotal year for Enanta as we execute on multiple catalysts across our pipeline, including progression of our RSV compounds and expansion of our immunology portfolio. Recruitment for RSVHR, our Phase 2 study of zelicapavir in high-risk adults infected with RSV, is ongoing and we plan to report topline data in the third quarter of this year. Following the encouraging results from our pediatric RSV study, we look forward to working with regulators to align on the registration pathway for zelicapavir in children and await the results of RSVHR, a Phase 3 enabling trial for adults. With both zelicapavir and EDP-323, we have the leading portfolio of RSV candidates in clinical development today and are eager to develop potential first-in-disease and best-in-class treatments for patients suffering from RSV,” said Jay R. Luly , Ph.D., President and Chief Executive Officer at Enanta Pharmaceuticals . “Moving forward, we will be exploring potential partnership opportunities to advance our RSV program. Simultaneously, we are working to ensure readiness for the next phase of RSV clinical development in a strategic and capital efficient manner, thereby extending our cash runway into fiscal 2028.” Dr. Luly added, “In parallel, we are rapidly advancing and expanding our immunology portfolio targeting Type 2 immune diseases, with an initial focus on indications with fast proof-of-concept. We are making progress to advance EPS-1421, our lead candidate for our KIT inhibition program, with the goal of developing a best-in-class, oral treatment for chronic spontaneous urticaria and other mast cell driven diseases. We are also excited about the progress in our STAT6 program, where we are leveraging our expertise in medicinal chemistry to develop novel, potent and selective oral inhibitors that block the IL-4/IL-13 signaling pathway, with an initial indication in atopic dermatitis and future expansion opportunities in asthma and other diseases. We expect to select a lead development candidate for STAT6 in the second half of this year and look forward to continuing to build out our immunology portfolio with the announcement of a third program this year. We have a busy year ahead with multiple opportunities to drive value for the company and move us closer to bringing important treatments to patients in need.” Fiscal First Quarter Ended December 31, 2024 Financial Results Total revenue for the three months ended December 31, 2024 was $17.0 million and consisted of royalty revenue from worldwide net sales of MAVYRET®/MAVIRET®, AbbVie’s eight-week treatment for chronic hepatitis C virus, compared to $18.0 million for the three months ended December 31, 2023 . The decrease in revenue is due to a decline in AbbVie’s sales of MAVYRET®/MAVIRET®. A portion (54.5%) of Enanta’s ongoing royalty revenue from AbbVie’s net sales of MAVYRET®/MAVIRET® is paid to OMERS, one of Canada’s largest defined benefit pension plans, pursuant to a royalty sale transaction affecting royalties earned after June 2023 . For financial reporting purposes, the transaction was treated as debt, with the upfront purchase payment of $200.0 million recorded as a liability. Each quarter, Enanta records 100% of the royalty earned as revenue and then amortizes the debt liability proportionally as 54.5% of the cash royalty payments are paid to OMERS through June 30, 2032 . This is subject to a cap of 1.42 times the purchase payment, after which point 100% of the cash royalty payments will be retained by Enanta. Interest expense was $2.0 million for the three months ended December 31, 2024 , as compared to interest expense of $3.4 million for the three months ended December 31, 2023 . Research and development expenses totaled $27.7 million for the three months ended December 31, 2024 , compared to $36.4 million for the three months ended December 31, 2023 . The decrease was due to a decrease in expenses for Enanta’s virology program due to timing of clinical trials in the company’s RSV program and to a lesser extent, a decrease in costs associated with Enanta’s COVID-19 program, as the company previously announced any further COVID-19 efforts would be in the context of collaborations. General and administrative expenses totaled $12.8 million for the three months ended December 31, 2024 , compared to $16.5 million for the three months ended December 31, 2023 . The decrease was due to a decrease in legal expenses related to the company’s patent infringement lawsuit against Pfizer. Interest and investment income, net, totaled $2.8 million for the three months ended December 31, 2024 , compared to $4.3 million for the three months ended December 31, 2023 . The decrease was due to lower cash and investment balances year-over-year. Enanta recorded an income tax benefit of $0.4 million for the three months ended December 31, 2024 , and $0.6 million for the three months ended December 31, 2023 . The income tax benefit in both periods was driven by interest earned on a pending $28 million federal income tax refund. Net loss for the three months ended December 31, 2024 was $22.3 million , or a loss of $1.05 per diluted common share, compared to a net loss of $33.4 million , or a loss of $1.58 per diluted common share, for the corresponding period in 2023. Enanta’s cash, cash equivalents and short-term marketable securities totaled $216.7 million at December 31, 2024 . Enanta expects that its current cash, cash equivalents and marketable securities, as well as its retained portion of future royalty revenue, will be sufficient to meet the anticipated cash requirements of its existing business and development programs into fiscal year 2028. Virology RSV Enanta aims to develop a first and leading RSV antiviral treatment portfolio to help all populations at high-risk for severe outcomes from RSV infection. This includes zelicapavir, Enanta’s lead, oral N-protein inhibitor, and EDP-323, its oral L-protein inhibitor, both of which received Fast Track designation from the U.S. Food and Drug Administration . Zelicapavir is being evaluated in RSVHR, a Phase 2b, randomized, double-blind, placebo-controlled study in adults with RSV infection who are at high risk of complications, including age over 65 years and/or those with congestive heart failure, chronic obstructive pulmonary disease or asthma. Enrollment in RSVHR is progressing, and the company is targeting completion in the current Northern Hemisphere RSV season with topline data in the third quarter of 2025. In December 2024 , Enanta announced results from a Phase 2 randomized, double-blind, placebo-controlled study in hospitalized and non-hospitalized pediatric RSV patients aged 28 days to 3 years old. In the study of 96 patients, an antiviral effect was observed for the primary and secondary virology endpoints in the overall pooled efficacy population. The primary endpoint in Part 2 of the study, which focused on virology, showed a pronounced antiviral effect with a 1.4 log decline in viral load at Day 5 compared to placebo. Additionally, a rapid and robust virologic effect was observed in a prespecified subset of patients who were randomized within 3 days of symptom onset, with a 1.2 log decline in viral load at Day 5 compared to placebo. The study also showed that zelicapavir demonstrated a favorable safety profile and was well-tolerated in this pediatric population. Enanta’s second clinical RSV candidate, EDP-323, is a novel oral, direct-acting antiviral selectively targeting the RSV L-protein. In September 2024 , Enanta announced positive results for EDP-323 in a Phase 2a challenge study of healthy adults infected with RSV, in which treatment with EDP-323 achieved highly statistically significant reductions in both viral load and clinical symptoms compared to placebo, as well as demonstrated a favorable safety and tolerability profile. With positive results from both zelicapavir and EDP-323, Enanta has the most advanced portfolio of RSV therapeutic candidates, which provides important optionality and the potential for first-in-disease and best-in-disease development strategies. The company expects to work with regulators to align on the registration pathway for zelicapavir in pediatric patients and will look to complete RSVHR, a Phase 3 enabling trial in high-risk adults. In addition, Enanta will evaluate potential partnership opportunities to advance its RSV assets to the next stage of clinical development. Zelicapavir is being evaluated in RSVHR, a Phase 2b, randomized, double-blind, placebo-controlled study in adults with RSV infection who are at high risk of complications, including age over 65 years and/or those with congestive heart failure, chronic obstructive pulmonary disease or asthma. Enrollment in RSVHR is progressing, and the company is targeting completion in the current Northern Hemisphere RSV season with topline data in the third quarter of 2025. In December 2024 , Enanta announced results from a Phase 2 randomized, double-blind, placebo-controlled study in hospitalized and non-hospitalized pediatric RSV patients aged 28 days to 3 years old. In the study of 96 patients, an antiviral effect was observed for the primary and secondary virology endpoints in the overall pooled efficacy population. The primary endpoint in Part 2 of the study, which focused on virology, showed a pronounced antiviral effect with a 1.4 log decline in viral load at Day 5 compared to placebo. Additionally, a rapid and robust virologic effect was observed in a prespecified subset of patients who were randomized within 3 days of symptom onset, with a 1.2 log decline in viral load at Day 5 compared to placebo. The study also showed that zelicapavir demonstrated a favorable safety profile and was well-tolerated in this pediatric population. Enanta’s second clinical RSV candidate, EDP-323, is a novel oral, direct-acting antiviral selectively targeting the RSV L-protein. In September 2024 , Enanta announced positive results for EDP-323 in a Phase 2a challenge study of healthy adults infected with RSV, in which treatment with EDP-323 achieved highly statistically significant reductions in both viral load and clinical symptoms compared to placebo, as well as demonstrated a favorable safety and tolerability profile. With positive results from both zelicapavir and EDP-323, Enanta has the most advanced portfolio of RSV therapeutic candidates, which provides important optionality and the potential for first-in-disease and best-in-disease development strategies. The company expects to work with regulators to align on the registration pathway for zelicapavir in pediatric patients and will look to complete RSVHR, a Phase 3 enabling trial in high-risk adults. In addition, Enanta will evaluate potential partnership opportunities to advance its RSV assets to the next stage of clinical development. In December 2024 , Enanta announced results from a Phase 2 randomized, double-blind, placebo-controlled study in hospitalized and non-hospitalized pediatric RSV patients aged 28 days to 3 years old. In the study of 96 patients, an antiviral effect was observed for the primary and secondary virology endpoints in the overall pooled efficacy population. The primary endpoint in Part 2 of the study, which focused on virology, showed a pronounced antiviral effect with a 1.4 log decline in viral load at Day 5 compared to placebo. Additionally, a rapid and robust virologic effect was observed in a prespecified subset of patients who were randomized within 3 days of symptom onset, with a 1.2 log decline in viral load at Day 5 compared to placebo. The study also showed that zelicapavir demonstrated a favorable safety profile and was well-tolerated in this pediatric population. Immunology Enanta’s immunology portfolio is focused on designing and developing highly potent and selective, oral small molecule inhibitors for the treatment of inflammatory diseases, by targeting key drivers of the type 2 immune response. KIT Inhibitors: EPS-1421, Enanta’s lead candidate, is a novel, potent and selective oral inhibitor of KIT, designed to treat chronic spontaneous urticaria and other indications by depleting mast cells, thereby addressing a primary driver of these diseases. EPS-1421 inhibits KIT with nanomolar potency in both binding and cellular assays, and has sub-nanomolar activity in vivo. EPS-1421 is also highly selective for KIT versus other kinases and, preclinically, has demonstrated good in vitro and in vivo ADME properties. Enanta is conducting scale-up activities and IND enabling studies in 2025. STAT6 Inhibitors: Enanta is advancing novel, potent and selective oral inhibitors of STAT6 for the treatment of type 2 immune driven diseases. The company will initially focus on atopic dermatitis and expand into other indications that block the IL-4/IL-13 signaling pathway, thereby addressing a primary driver of these diseases. Enanta’s prototype inhibitors demonstrate potent activity and high selectivity for STAT6 over other STATs in both biochemical and cellular assays. Additionally, the prototype inhibitors demonstrate systemic in vivo target engagement after ex vivo IL-4 stimulation. The company is conducting lead optimization activities and plans to select a STAT6 lead candidate in the second half of 2025. Enanta plans to expand its presence in immunology with the introduction of a third program in 2025. KIT Inhibitors: EPS-1421, Enanta’s lead candidate, is a novel, potent and selective oral inhibitor of KIT, designed to treat chronic spontaneous urticaria and other indications by depleting mast cells, thereby addressing a primary driver of these diseases. EPS-1421 inhibits KIT with nanomolar potency in both binding and cellular assays, and has sub-nanomolar activity in vivo. EPS-1421 is also highly selective for KIT versus other kinases and, preclinically, has demonstrated good in vitro and in vivo ADME properties. Enanta is conducting scale-up activities and IND enabling studies in 2025. STAT6 Inhibitors: Enanta is advancing novel, potent and selective oral inhibitors of STAT6 for the treatment of type 2 immune driven diseases. The company will initially focus on atopic dermatitis and expand into other indications that block the IL-4/IL-13 signaling pathway, thereby addressing a primary driver of these diseases. Enanta’s prototype inhibitors demonstrate potent activity and high selectivity for STAT6 over other STATs in both biochemical and cellular assays. Additionally, the prototype inhibitors demonstrate systemic in vivo target engagement after ex vivo IL-4 stimulation. The company is conducting lead optimization activities and plans to select a STAT6 lead candidate in the second half of 2025. Enanta plans to expand its presence in immunology with the introduction of a third program in 2025. EPS-1421, Enanta’s lead candidate, is a novel, potent and selective oral inhibitor of KIT, designed to treat chronic spontaneous urticaria and other indications by depleting mast cells, thereby addressing a primary driver of these diseases. EPS-1421 inhibits KIT with nanomolar potency in both binding and cellular assays, and has sub-nanomolar activity in vivo. EPS-1421 is also highly selective for KIT versus other kinases and, preclinically, has demonstrated good in vitro and in vivo ADME properties. Enanta is conducting scale-up activities and IND enabling studies in 2025. Enanta is advancing novel, potent and selective oral inhibitors of STAT6 for the treatment of type 2 immune driven diseases. The company will initially focus on atopic dermatitis and expand into other indications that block the IL-4/IL-13 signaling pathway, thereby addressing a primary driver of these diseases. Enanta’s prototype inhibitors demonstrate potent activity and high selectivity for STAT6 over other STATs in both biochemical and cellular assays. Additionally, the prototype inhibitors demonstrate systemic in vivo target engagement after ex vivo IL-4 stimulation. The company is conducting lead optimization activities and plans to select a STAT6 lead candidate in the second half of 2025. Corporate On February 3, 2025 , Enanta filed a notice of appeal with the United States Court of Appeals for the Federal Circuit related to a June 2022 lawsuit the company filed in the United States District Court for the District of Massachusetts against Pfizer, Inc. seeking damages for infringement of U.S. Patent No. 11,358,953 (the ’953 Patent) in the manufacture, use and sale of Pfizer’s COVID-19 antiviral, Paxlovid™ (nirmatrelvir tablets; ritonavir tablets). Enanta plans to issue its fiscal second quarter financial results press release on May 12, 2025 . About Enanta Pharmaceuticals, Inc. Enanta is using its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs with an emphasis on indications in virology and immunology. Enanta’s clinical programs are currently focused on respiratory syncytial virus (RSV) and its earlier-stage immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, including KIT and STAT6 inhibition. Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing chronic hepatitis c virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET® ( U.S. ) and MAVIRET® (ex- U.S. ) (glecaprevir/pibrentasvir). A portion of Enanta’s royalties from HCV products developed under its collaboration with AbbVie contribute ongoing funding to Enanta’s operations. Please visit www.enanta.com for more information. Forward Looking Statements This press release contains forward-looking statements, including statements with respect to the prospects for advancement of Enanta’s clinical programs in RSV and its preclinical programs targeting KIT and STAT6 inhibition. Statements that are not historical facts are based on management’s current expectations, estimates, forecasts and projections about Enanta’s business and the industry in which it operates and management’s beliefs and assumptions. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors and risks that may affect actual results include: the impact of development, regulatory and marketing efforts of others with respect to vaccines and competitive treatments for RSV; the discovery and development risks of Enanta’s programs in virology and immunology; Enanta’s lack of clinical development experience; Enanta’s need to attract and retain senior management and key research and development personnel; Enanta’s need to obtain and maintain patent protection for its product candidates and avoid potential infringement of the intellectual property rights of others; and other risk factors described or referred to in “Risk Factors” in Enanta’s Form 10-K for the fiscal year-ended September 30, 2024 , and any other periodic reports filed more recently with the Securities and Exchange Commission . Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Enanta undertakes no obligation to update or revise these statements, except as may be required by law. Tables to Follow 2024 2023 $ 16,959 $ 18,003 27,656 36,371 12,846 16,518 40,502 52,889 (23,543 ) (34,886 ) (1,962 ) (3,441 ) 2,799 4,298 (22,706 ) (34,029 ) 416 622 $ (22,290 ) $ (33,407 ) $ (1.05 ) $ (1.58 ) $ (1.05 ) $ (1.58 ) 21,238 21,088 21,238 21,088 2024 2024 $ 84,349 $ 37,233 132,342 210,953 7,718 6,646 10,684 12,413 32,444 31,999 608 608 268,145 299,852 37,368 32,688 39,675 40,658 3,360 3,360 94 94 $ 348,642 $ 376,652 $ 4,726 $ 8,002 10,575 13,547 32,743 34,462 1,006 1,524 49,050 57,535 129,738 134,779 56,453 53,943 1,350 1,350 235 231 236,826 247,838 111,816 128,814 $ 348,642 $ 376,652 View source version on businesswire.com: https://www.businesswire.com/news/home/20250210108421/en/ Media and Investors Contact: Jennifer Viera jviera@enanta.com Source: Enanta Pharmaceuticals, Inc.

Phase 2Clinical ResultFinancial Statement

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Indication	Highest Phase	Country/Location	Organization	Date
COVID-19	Phase 3	Mexico	Pfizer Inc.	16 Jul 2021
COVID-19	Phase 3	Hungary	Pfizer Inc.	16 Jul 2021
COVID-19	Phase 3	Bulgaria	Pfizer Inc.	16 Jul 2021
COVID-19	Phase 3	United States	Pfizer Inc.	16 Jul 2021
COVID-19	Phase 3	Puerto Rico	Pfizer Inc.	16 Jul 2021
COVID-19	Phase 3	South Africa	Pfizer Inc.	16 Jul 2021
COVID-19	Phase 3	Japan	Pfizer Inc.	16 Jul 2021
COVID-19	Preclinical	South Korea	Pfizer Inc.	16 Jul 2021
COVID-19	Preclinical	Turkey	Pfizer Inc.	16 Jul 2021
COVID-19	Discovery	Turkey	Pfizer Inc.	16 Jul 2021

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Study	Phase	Population	Analyzed Enrollment	Group	Results	Evaluation	Publication Date


NCT05567952 (CTgov)	Phase 2	COVID-19	436	Nirmatrelvir+Ritonavir (Nirmatrelvir 300 mg + Ritonavir 100 mg)	afsryiamar(ahhtmhnpzb) = chujlcxgpj agamotxbtq (nctytgedku, tqoycgprfn - efkezmdciz) View more	-	08 Oct 2024
				Placebo+Ritonavir (Placebo + Ritonavir 100 mg)	afsryiamar(ahhtmhnpzb) = aetwxsxlzc agamotxbtq (nctytgedku, zsdykoisbw - iumoiwkdtm) View more
NCT05576662 (STOP-PASC, CTgov)	Phase 2	Post Acute COVID 19 Syndrome	168	Nirmatrelvir+Ritonavir (Nirmatrelvir Plus Ritonavir)	lpbqgnoofq(xtapcrmoim) = xpzocuacih abspptvuhc (tflzydqyeh, qqgehinfox - trlsnmbmtg) View more	-	25 Sep 2024
				Placebo+Ritonavir (Placebo Plus Ritonavir)	lpbqgnoofq(xtapcrmoim) = mlqlcgbkfv abspptvuhc (tflzydqyeh, ctjqffgvzh - tqqrxdppbr) View more
NCT05487040 (CTgov)	Phase 1	COVID-19	15	PF-07321332 (nirmatrelvir)+ritonavir (Cohort 1 (No HD))	lxdbhfwlvb(tfvtkkufvn) = ktcfhlqjvv ytkbtbdbcf (bibidnivnr, ykirrnnmuc - cxbuscampj) View more	-	23 Sep 2024
				PF-07321332 (nirmatrelvir)+ritonavir (Cohort 2 (Intermittent HD))	lxdbhfwlvb(tfvtkkufvn) = xdruztrvvv ytkbtbdbcf (bibidnivnr, dboxqyunyt - zdyqmvneet) View more
NCT05438602 (CTgov)	Phase 2	COVID-19	158	Placebo+Nirmatrelvir+Ritonavir (Nirmatrelvir + Ritonavir 5 Day Then Placebo 10 Day)	ipykjrymuj(tlafdwnpqp) = ssfiritloh itholkcuii (brhprukqod, pxxxbcwjxk - qwuyymaxmg) View more	-	23 Sep 2024
				Placebo+Nirmatrelvir+Ritonavir (Nirmatrelvir + Ritonavir 10 Day Then Placebo 5 Day)	ipykjrymuj(tlafdwnpqp) = dqhwoplram itholkcuii (brhprukqod, ufdlyshucz - gdxhoguqul) View more
NCT05011513 (EPIC-SR, Pubmed) Manual	Phase 2/3	COVID-19	1,288	Nirmatrelvir-riritonavir	tljobxknwc(jkwuglbunp) = pcxrycnyxe xxgheoocym (qsjlfmojuw ) View more	Negative	04 Apr 2024
				Placebo	tljobxknwc(jkwuglbunp) = lrvmqcbruu xxgheoocym (qsjlfmojuw ) View more
NCT05005312 (CTgov)	Phase 1	Liver Injury	17	PF-07321332+ritonavir (Normal Hepatic Function)	hgxtaqodli(oaawtaigge) = hbkrberste qssxshdokp (nymryylfmv, eldeojqdwy - hnvkielwks) View more	-	06 Sep 2023
				PF-07321332+ritonavir (Moderate Hepatic Impairment)	hgxtaqodli(oaawtaigge) = aclwoslxbg qssxshdokp (nymryylfmv, vblxirhxbi - bjywuvymdv) View more
NCT05011513 (EPIC-SR, CTgov)	Phase 2/3	COVID-19	1,440	Placebo	semuxudjbs(sfpxbeknir) = antgmwlioh thbtkplbxr (assejakmlz, pxfzxcnrxk - yanndcxjax) View more	-	14 Aug 2023
NCT04960202 (phase 3 randomized trial \| EPIC-HR, CTgov)	Phase 2/3	COVID-19	2,246	Placebo	ovoszdekqk(uiphwwungz) = qzhjqoskac cbcwytfsby (njhbllwiwv, woifwsqwwf - ezmxkhakwj) View more	-	09 Feb 2023
NCT04960202 (EPIC-HR, Pubmed) Manual	Phase 3	COVID-19	2,246	Nirmatrelvir+Ritonavir	hzhzlyyljy(mrkerepmrt) = sltyrndpxg tsnaehtryu (behrrnycub ) View more	Positive	16 Feb 2022
				Placebo	hzhzlyyljy(mrkerepmrt) = ihpgdofcxq tsnaehtryu (behrrnycub ) View more

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