Preliminary results from two trials showed that GSK’s respiratory syncytial virus (RSV) vaccine Arexvy has potential in younger adults with certain risk factors, potentially positioning the shot for a larger population.

The results come two days after the FDA approved Pfizer’s RSV vaccine Abrysvo for adults ages 18 to 59 who are at an increased risk of developing lower respiratory tract disease (LRTD), making it the first RSV shot for adults of all ages who are at risk. The FDA has endorsed Arexvy for patients 60 and older and for those 50 to 59 who are at increased risk of severe disease.

In one of the new Arexvy trials, a single dose triggered robust immune responses in patients age 18 to 49 who are at increased risk for LRTD due to at least one underlying medical condition. The immune response in the 395 participants was non-inferior to that seen in a group of 417 individuals age 60 and older, allowing the trial to succeed on both of its primary endpoints.

In the other study, a single dose of Arexvy provided a robust immune response in 131 immunocompromised adults who have had a kidney or lung transplant. In those adults, a second dose of Arexvy elicited responses similar to those in a group of 125 healthy individuals age 50 and older who received one shot. 

The preliminary results are being presented Thursday at the CDC’s Advisory Committee on Immunization Practices (ACIP) meeting.

“These promising data add to the evidence supporting GSK’s RSV vaccine and could help expand protection to more adults at risk from RSV disease,” the company’s chief scientific officer, Tony Wood, Ph.D., said in a release. “They also provide valuable insights into the potential impact of a second dose for certain populations.”

Final results from the trials will be presented at upcoming medical conferences and will be submitted to regulators to support potential label updates, GSK added.

Despite the nods from the FDA for both RSV vaccines, the CDC has not followed suit. Four months ago, the agency narrowed its recommendation for RSV vaccines to adults age 75 and older and those between the ages of 60 and 74 who are at risk of severe disease. The CDC had previously recommended the shots for people 60 and older after a consultation with their doctors.

Last year, while Pfizer’s Abrysvo generated sales of $890 million, GSK reported that revenue from Arexvy reached 1.2 billion pounds sterling ($1.5 billion). After the CDC’s narrowed recommendation, GSK reduced its projection for 2024 sales from a high single- to low double-digit percentage growth to a low- to mid-single-digit percentage growth.

In addition to Abrysvo and Arexvy, there is a new entrant in the RSV adult market as Moderna scored FDA approval for its vaccine mRESVIA five months ago. That nod covers patients 60 and older.