Gilead Sciences has blamed the low rate of respiratory syncytial virus (RSV) infections last season for ending two midstage trials of obeldesivir.
The pharma had been evaluating the antiviral drug in two RSV studies in adults and children, respectively. However, the company “recently terminated the two trials following lower than expected RSV incidence rates during the most recent RSV season in the Northern Hemisphere, which made it difficult to determine meaningful rates of symptom reduction, a primary endpoint of the study,” Gilead confirmed to Fierce Biotech.
The decision to stop the studies “did not reflect any safety or efficacy concerns,” added Gilead, which will share data already accumulated from the trials to “inform a discussion on potential next steps.”
With no other RSV candidates listed in Gilead’s pipeline, the decision on whether to persevere with obeldesivir in this indication will determine whether the company still has a place in the RSV antiviral race.
It’s not the first time low infection rates have derailed a trial of obeldesivir. Back in 2023, Gilead ended a phase 3 study of the antiviral for COVID-19 based on “lower-than-expected COVID-19 incidence rates and related hospitalizations.”
A clinical trial of obeldesivir in Marburg virus, a severe disease that can have a high death rate, is ongoing, Gilead pointed out. Preclinical research has suggested that the antiviral could prove effective against the virus.
The RSV market is dominated by vaccines like Pfizer’s Abrysvo and GSK’s Arexvy and Moderna’s mRESVIA along with Sanofi and AstraZeneca’s prophylactic antibody Beyfortus. Merck’s own antibody option Enflonsia has recently secured approval.
Meanwhile, a number of companies have demonstrated clinical success with their antiviral candidates in recent months, including Shionogi’s S-337395 and Enanta Pharmaceuticals’ zelicapavir. Despite the dominance of vaccines, 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.