At the 44th Annual J.P. Morgan Healthcare Conference, Enanta Pharmaceuticals discussed its respiratory syncytial virus (RSV) portfolio and the need for an RSV treatment. RSV causes severe lung infections, including bronchiolitis and pneumonia, and is a leading cause of hospitalisation in infants. Populations at higher risk for severe illness include infants and young children, adults over 65 years of age, and adults with immunocompromising conditions such as HIV, transplant recipients, or those with pre-existing comorbidities such chronic obstructive pulmonary disease (COPD) and asthma. RSV innovation has accelerated at an unprecedented pace in recent years, due to the launch of several novel prophylactic monoclonal antibodies (mAbs) and vaccines. However, there has been a sub-optimal adoption of adult prophylactic vaccines in the US, largely because they have not been recommended for all US Food and Drug Administration (FDA)-approved patient groups. Furthermore, paediatric prophylaxis largely relies on mAbs and these therapies only provide passive immunity and do not provide long term protection. In addition, the antibody approach has a low barrier for resistance. Therefore, there still is opportunity for breakthrough infections to occur and the burden of disease remains high. In addition, while several prophylactic options are now available, there are currently no safe and effective treatments that have been approved for this indication and thus there is a large unmet need for novel therapeutics. Patients who develop severe RSV continue to rely on supportive care.
Enanta has a leading portfolio of RSV replication inhibitors with potential for first-in-disease (zelicapavir), and best-in-disease (EDP-323) treatment, and the ability for combination. Zelicapavir and EDP-323 are direct acting antivirals in Phase II development. They target the N-protein and L-protein, respectively, both of which are essential for RSV replication. According to GlobalData’s analyst consensus forecast, zelicapavir could reach $290m in global sales by 2031, if approved.
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A Phase IIb study, which evaluated the efficacy and safety of zelicapavir in adults with acute RSV infection who are at high risk of complications (including the elderly and/or those with congestive heart failure (CHF), COPD or asthma), demonstrated promising results. Zelicapavir demonstrated compelling results on multiple clinically meaningful and potential registrational endpoints measuring different aspects of RSV disease; up to one week improvement in complete Respiratory Infection Intensity and Impact Questionnaire (RiiQ) symptom resolution, statistically significant improvement in patient-global impression of severity score (PGI-s), and a lower hospitalisation rate in drug-treated group. This data has supported advancement of zelicapavir into a Phase III study of high-risk adults. Another Phase II paediatric study treating children as young as 28 days of age, showed that zelicapavir was well-tolerated in infants, with a favourable safety profile. An antiviral effect was also observed for the primary and secondary virology endpoints in the overall population. A subset of subjects who started treatment within three days of symptom onset experienced a 1.2 log decline in viral load, indicating a rapid antiviral response. This data supports further clinical development of zelicapavir in paediatrics.
Enanta also highlighted its other RSV asset, EDP-323. In a Phase IIa RSV challenge study EDP-323 was well-tolerated with a safety profile similar to placebo. Primary and key secondary endpoints were achieved with high statistical significance at both dose levels compared to placebo; reduction in viral load of 85–87%, reduction in viral culture of 97–98%, and alleviation of clinical symptoms by 66–78%. This data also supports further clinical development of EDP-323.
The above data shows promise for future available treatments for RSV disease, with the hope that these treatments will alleviate the burden of RSV infection. Enanta is positioned to be a leader in the RSV therapeutic market, with two strong assets, applicable to both the paediatric and high-risk adult cohort.
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