Pfizer grows investigational RSV vaccine programmes with acquisition of ReViral

Pzifer’s acquisition of ReViral will include its portfolio of promising therapeutic candidates, such as sisunatovir, an orally administered inhibitor designed to block fusion of the RSV virus to the host cell.


Pfizer is to acquire ReViral, a privately held, clinical-stage biopharmaceutical company focused on discovering, developing, and commercialising novel antiviral therapeutics that target respiratory syncytial virus (RSV).

“At Pfizer, we have a strong heritage in, and commitment to, fighting infectious diseases, most recently evidenced by our delivery of the first authorised vaccine and oral therapy to combat COVID-19,” commented Albert Bourla, Chairman and Chief Executive Officer, Pfizer. “We are continuing to grow our pipeline – through our own research-and-development efforts, such as our investigational RSV vaccine programmes, as well as strategic investments in companies like ReViral – with a focus on end-to-end capabilities to help protect patients from severe illness, hospitalisation, and death.”

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.

ReViral has a portfolio of promising therapeutic candidates, including sisunatovir, an orally administered inhibitor designed to block fusion of the RSV virus to the host cell. Sisunatovir significantly reduced viral load in a Phase II RSV human challenge study in healthy adults and is currently in Phase II clinical development in infants. The development programme for sisunatovir is expected to continue in both adult and paediatric populations. A second programme is focussed on the inhibition of RSV replication targeting the viral N protein. The lead candidate in this programme is currently in Phase I clinical development.

“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,” stated Dr Annaliesa Anderson, Senior Vice President and Chief Scientific Officer, Bacterial Vaccines and Hospital, at Pfizer. Combining the capabilities and expertise of our organisations 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 US Food and Drug Administration (FDA). In June 2021, ReViral announced the successful completion of Part A of the Phase II REVIRAL1 study of sisunatovir for the treatment of RSV infections in hospitalised 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 one and 36 months hospitalised with RSV LRTIs. Following a thorough review by the REVIRAL1 Data Safety Monitoring Committee, sisunatovir showed a favourable 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.

“ReViral’s mission has always been to develop world-class therapies for RSV patients,” stated Alex Sapir, CEO, ReViral. “This acquisition represents a validation of the deep antiviral experience of the ReViral team and our unwavering commitment to deliver therapies for patients in need. Pfizer is an optimal partner given their commitment to RSV through their ongoing RSV vaccine programme, coupled with their world-class clinical, regulatory, manufacturing and commercial capabilities. We look forward to working with our colleagues at Pfizer to bring these therapies to patients as quickly as possible.”

Under the terms of the agreement, Pfizer will acquire ReViral for a total consideration of up to $525 million, including upfront and development milestones.