Pfizer Announces Positive Top-Line Results from Phase 3 Study of ABRYSVO in Adults Aged 18 to 59 at Increased Risk for RSV Disease

Pfizer Inc. announced positive top-line immunogenicity and safety data from the ongoing pivotal Phase 3 clinical trial (NCT05842967) MONeT (RSV IMmunizatiON Study for AdulTs at Higher Risk of Severe Illness),evaluating a single dose of ABRYSVO versus placebo in adults 18 to 59 years of age at risk of developing severe respiratory syncytial virus (RSV)-associated lower respiratory tract disease (LRTD).

Adults with certain underlying chronic conditions are at increased risk of developing, and being hospitalized for, RSV-associated LRTD. Among US adults 18 to 49 years of age, 9.5 percent have a chronic condition that puts them at risk of severe RSV disease and this percentage rises to 24.3 percent among persons 50 to 64 years of age. However, no RSV vaccines have been approved for use in adults 18 to 59 years of age. The MONeT study was initiated to address this significant unmet need by investigating the immunogenicity and safety of ABRYSVO in adults aged 18 to 59 at increased risk for RSV disease, such as those with asthma, diabetes, and chronic obstructive pulmonary disease.

The MONeT study achieved its co-primary immunogenicity endpoints and primary safety endpoint:

• Participants demonstrated RSV-A and RSV-B subgroup neutralizing responses non-inferior to the response seen in the Phase 3 (NCT05035212) RENOIR study of ABRYSVO in more than 34,000 adults aged 60 or older where vaccine efficacy was previously demonstrated.
• Participants also achieved at least a four-fold increase in serum neutralizing titers for RSV-A and RSV-B one month following receipt of ABRYSVO compared to pre-vaccination.
• During the trial, ABRYSVO was well-tolerated, and safety findings were consistent with those from previous investigations of ABRYSVO in other populations.

Pfizer also met its diversity recruitment goals for the study providing data from participants that mirror the diverse U.S. population and had a balanced representation across underlying medical conditions.

Pfizer intends to submit these data to regulatory agencies and request expansion of the age group from the current indication to 18 years of age and older. The use of immunobridging studies to extrapolate efficacy from older to younger adults is an established regulatory pathway.⁴ The company also intends to publish these findings in a peer-reviewed scientific journal and share them at an upcoming scientific conference.

“These encouraging results provide evidence that ABRYSVO can help protect adults with increased risk against RSV-associated illness,” said Annaliesa Anderson, Ph.D., Senior Vice President and Head, Vaccine Research and Development, Pfizer. “We are excited to address a significant unmet need, pending regulatory authority approval, as ABRYSVO has the potential to become the first and only RSV vaccine for adults 18 years and older.”