Pfizer’s respiratory syncytial virus (RSV) vaccine Abrysvo has shown efficacy in immunocompromised adults, the pharma announced Monday.

In substudy B of Pfizer’s ongoing Phase 3 MONeT trial, Abrysvo was well-tolerated and showed a consistent safety profile among the 203 participants.

The trial focused on investigating two doses, given one month apart, in adults who are immunocompromised — meaning those at risk of developing RSV-associated lower respiratory tract disease, or LRTD.

The trial measured the vaccine’s impact among four groups: patients with non-small cell lung cancer, patients with end-stage renal disease on hemodialysis, patients with autoimmune inflammatory disorder who are receiving active immunomodulator therapy, as well as patients who are solid organ transplant recipients.

A single 120 µg dose of Abrysvo resulted in a hefty neutralizing response against both RSV-A and RSV-B subtypes of the virus, Pfizer said in a press release. The pharma giant is set to discuss the findings at an upcoming scientific meeting and submit them for regulatory review for an expanded label.

While immunocompromised adults are far more likely to develop severe complications from RSV, there’s currently no vaccine available for people between the ages of 18 to 59 in the U.S. 

Abrysvo is approved by the Food and Drug Administration for adults over the age of 60. Last year, the agency approved the vaccine for pregnant people as a preventive measure for infants aged 0 to six months old.

“We are encouraged by the positive top-line data from this study, which provide important evidence that Abrysvo has the potential to address a significant unmet need in this vulnerable population,” said Annaliesa Anderson, SVP and chief scientific officer of vaccine research and development at Pfizer, in a statement.

RSV is one of the areas that mRNA vaccine makers like Moderna and Pfizer have been focused on pivoting to as their COVID-19 product sales continue to decline. 

Some of Pfizer’s competitors in the space include GSK, which recently won an approval for Arexvy in adults between the ages of 50 and 59 who are at risk of severe RSV, as well as those over the age of 60.

In May, the FDA also approved Moderna’s mRNA RSV vaccine mRESVIA for people aged 60 to 74 who are at higher risk of developing severe RSV.

Sanofi and AstraZeneca’s monoclonal antibody Beyfortus, meanwhile, gained approval last year for RSV prevention in children under the age of two.

Despite facing a drop in COVID-19 sales in recent years, Pfizer reported a 3% increase in year-over-year revenue in its latest earnings report, and raised its full-year guidance by $1 billion to a range of $59.5 billion to $62.5 billion.