Pfizer Halts Development of Sisunatovir, Writing Off $525 Million ReViral Acquisition

　　【Pharmaceutical Network Industry DynamicsTwo years ago (2022), Pfizer, a leading pharmaceutical company, spent $525 million to acquire ReViral, a biotechnology company dedicated to antiviral treatments for respiratory syncytial virus (RSV), and obtained the latter's oral inhibitor Sisunatovir. This drug aims to block RSV replication by inhibiting the fusion of the virus with host cells mediated by the F protein. However, Pfizer has recently announced the termination of the development of Sisunatovir.
 

According to a statement by a Pfizer spokesperson in an email, the clinical development of Sisunatovir has faced "multiple challenges," including drug interactions with antacids. Despite Pfizer's continued efforts to address these challenges, the company has decided to halt the development of Sisunatovir in order to focus on identifying and advancing other investigational therapeutic candidates with the greatest potential for preventing and treating RSV disease and other viral respiratory pathogens.
 

As of now, both ongoing trials of Sisunatovir have been terminated, including a Phase 2/3 trial that enrolled adult patients with RSV and a Phase 1 trial targeting infants and children with RSV-related pneumonia. It is understood that the FDA had previously granted Fast Track designation to both trials, and the results were originally expected to be announced in September this year. With Pfizer's decision to terminate these trials, it means they will no longer proceed.
 

Notably, in addition to Sisunatovir, another RSV candidate drug from ReViral, PF-07923567 (RV-299), was also abandoned by Pfizer in August 2023.
 

Data show that PF-07923567 (RV-299) is a small molecule RSV N-protein replication inhibitor currently in Phase I trials. In April 2022, Pfizer acquired ReViral and obtained multiple RSV therapeutic candidates, including RV-299.
 

On August 1, 2023, Pfizer updated its R&D pipeline, removing the Phase II project pneumococcal vaccine PF-06842433 and the GLP-1R small molecule agonist lotiglipron from the pipeline. At the same time, the development plans for several Phase I projects, including the oral RSV inhibitor RV-299 acquired through the acquisition of ReViral, were also terminated.
 

At this point, Pfizer will no longer have any ongoing oral RSV projects. In the RSV field, Pfizer only retains an early-stage combination vaccine for RSV and influenza, PF-07941314.
 

As a widely spread virus, RSV poses a significant health threat to infants, the elderly, and individuals with compromised immune systems, also imposing a heavy burden on society and families. Vaccines are crucial tools for preventing viral infections, and the respiratory syncytial virus (RSV) vaccine market is considered to have immense potential, attracting major pharmaceutical companies such as GSK, Moderna, and Pfizer to enter the field.
 

In terms of the number of people vaccinated with the RSV vaccine, following the U.S. Centers for Disease Control and Prevention (CDC) narrowing its recommendation in June this year regarding RSV vaccination for the elderly, it has temporarily advised against the use of these vaccines in adults under 60. The CDC recommends that individuals aged 75 and above, as well as those aged 60 to 74 who are at high risk, receive the RSV vaccine. A single dose of this vaccine can provide protection for multiple years. This decision has led to a decline in demand for the RSV vaccine. Analysts have pointed out that GSK’s Arexvy, which was approved in the U.S. in May last year, may see lower-than-expected sales in the third quarter compared to Wall Street forecasts; this is also the world's first RSV vaccine. However, GSK still expects Arexvy’s annual sales to peak at $3.92 billion.
 

Data shows that in 2023, GSK's RSV vaccine sales reached $1.564 billion, while Pfizer achieved only $890 million in sales. However, the market expects GSK’s sales this year to slightly decline to around $1.5 billion, whereas Pfizer’s sales are projected to grow by nearly 40%, reaching $1.2 billion.
 

Disclaimer: In any case, the information or opinions expressed in this article do not constitute investment advice to any person.