Positive top-line results from phase III study of Abrysvo in adults aged 18 to 59 at increased risk for RSV disease – Pfizer

Pfizer Inc. announced positive top-line immunogenicity and safety data from the ongoing pivotal Phase III 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 Abvrysvo 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 : i.Participants demonstrated RSV-A and RSV-B subgroup neutralizing responses non-inferior to the response seen in the Phase III (NCT05035212) RENOIR study of Abrysvo in more than 34,000 adults aged 60 or older where vaccine efficacy was previously demonstrated. ii. 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. iii. 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. The company also intends to publish these findings in a peer-reviewed scientific journal and share them at an upcoming scientific conference.

ABOUT MONeT : MONeT (RSV IMmunizatiON Study for AdulTs at Higher Risk of Severe Illness ) is a Phase III, multicenter clinical trial (NCT05842967) investigating the safety, tolerability and immunogenicity of Abrysvo in adults at risk of RSV-associated disease, including adults with certain chronic medical conditions (substudy A) and adults who are immunocompromised (substudy B). Substudy A is a double-blinded study that randomized 681 adults aged 18 to 59 with chronic conditions, with 2:1 to receive a single dose of Abrysvo or placebo. Substudy B is an open-label study that enrolled approximately 200 immunocompromised adults aged 18 or older, roughly half of which were aged 60 or older, who received two doses of Abrysvo, one month apart.