Enanta Pharmaceuticals’ respiratory syncytial virus (RSV) antiviral reduced the viral load in a phase 2 study in children, maintaining hopes the biotech can find a niche in a market now dominated by Big Pharma vaccines.
The company tested its N-protein inhibitor zelicapavir in 96 children aged between 28 days and 36 months with RSV who were either hospitalized or non-hospitalized. The study was split into two parts, which each involved patients receiving zelicapavir or placebo once daily for five days.
Investigators observed an antiviral effect on the primary and secondary virology endpoints in the overall pooled efficacy population, the biotech said in a release, with the drop in viral load peaking at a 0.7 log decline on Day 9.
However, the company emphasized that the primary endpoint in the second part of the study “showed a more pronounced effect.” Specifically, this second cohort saw a viral load decline of 1 log by Day 3 and 1.4 log by Day 5 when compared to placebo.
In a prespecified group of patients who were randomized within three days of symptom onset, investigators recorded a 1.2 log decline in viral load at Day 5 compared to placebo, Enanta said in the release, describing this as a "rapid and robust virologic effect."
The readout appeared to meet the expectations of analysts at Evercore ISI, who said in a Monday morning note that they had been “looking for a 1 log reduction in viral load over placebo, the benchmark derived from a study of ArkBio’s ziresovir.”
In its release, Enanta also pointed out that zelicapavir had demonstrated a favorable safety profile and that there were no discontinuations caused by adverse events.
“These data provide us with continued confidence in zelicapavir and valuable insights to inform the design of a potential registration enabling trial,” Enanta Chief Medical Officer Scott Rottinghaus, M.D., said in the Dec. 9 release. “There is a substantial need for safe and effective oral treatments for RSV, and we believe that these important antiviral data along with the favorable safety profile observed in this young, vulnerable population support further clinical evaluation of zelicapavir.”
Today’s readout comes a couple of months after Enanta’s L-protein inhibitor, dubbed EDP-323, scored its own phase 2 win in RSV. That EDP-323 study raised “the high bar set by zelicapavir,” the company said at the time.
Enanta is also evaluating zelicapavir in a phase 2b study in the elderly and/or those with congestive heart failure, chronic obstructive pulmonary disease or asthma.
The compounds are moving toward a market that is already served by RSV vaccines like Pfizer’s Abrysvo, which can prevent infection and, in doing so, reduce the number of people who may need an antiviral. However, Enanta has previously explained that it sees an ongoing need for antivirals in both the pediatric and adult populations, noting babies and children will go on to get RSV infection after protection wanes and that there is low vaccine use in adults.