Pfizer already has an RSV vaccine candidate for older adults in Phase 3 trials: and the acquisition of ReViral gives it a portfolio of ‘promising’ therapeutic candidates, including sisunatovir, an orally-administered inhibitor designed to block fusion of the RSV virus to the host cell.
Pfizer believes the company, which is based at the Stevenage Bioscience Catalyst in the UK and Research Triangle Park in North Carolina, has the potential to create annual revenue from its programs of $1.5bn or more.
Sisunatovir Phase 2 results
RSV is a respiratory pathogen, which can lead to severe and life-threatening lower respiratory tract infections (LRTIs) in high-risk populations, including young infants, immunocompromised individuals, and older adults. It is estimated to cause infections in approximately 64 million people, resulting in about 160,000 deaths, globally each year.
Sisunatovir ‘significantly reduced’ viral load in a phase 2 RSV human challenge study in healthy adults and is currently in phase 2 clinical development in infants.
The development program for sisunatovir is expected to continue in both adult and pediatric populations.
A second program is focused on the inhibition of RSV replication targeting the viral N protein. The lead candidate in this program is currently in phase 1 clinical development.
“Currently, treatment options for RSV are extremely limited and focus primarily on supportive care,” said Annaliesa Anderson, Ph.D., senior vice president and chief scientific officer, bacterial vaccines and hospital, Pfizer.
“The proposed acquisition of ReViral’s pipeline of therapeutic candidates is complementary to our efforts to advance the first vaccine candidate to help protect against this harmful disease. Combining the capabilities and expertise of our organizations will enable us to further the clinical development of a potential therapy for those with RSV disease.”
Sisunatovir has been granted Fast Track designation by the FDA. In June 2021, ReViral announced the successful completion of Part A of the phase 2 REVIRAL1 study of sisunatovir for the treatment of RSV infections in hospitalized infants.
REVIRAL1 is a global three-part adaptive study to evaluate the safety, tolerability, pharmacokinetic (PK) profile, antiviral effects, and clinical effect of single and multiple oral doses of sisunatovir in otherwise healthy infants between the ages of 1 and 36 months hospitalized with RSV LRTIs.
Following a review by the REVIRAL1 Data Safety Monitoring Committee, sisunatovir showed a favorable safety and PK exposure profile to advance to Part B, the double-blind, placebo-controlled stage of the study where patients receive drug or placebo twice a day for five days.