Pfizer’s ABRYSVO® Shows Promising Results in Phase 3 Trial Targeting RSV Prevention in High-Risk Adults

Pfizer has announced encouraging findings from its ongoing pivotal Phase 3 clinical trial, known as MONeT (RSV IMmunizatiON Study for AdulTs at Higher Risk of Severe Illness), evaluating the efficacy and safety of ABRYSVO in adults at risk of severe respiratory syncytial virus (RSV)-associated lower respiratory tract disease (LRTD). Looking ahead, Pfizer plans to submit the compelling data to regulatory agencies with the aim of expanding the age indication to encompass individuals aged 18 to 59.

ABRYSVO is a bivalent vaccine that was designed to provide broad protection against all RSV-LRTD, regardless of the virus subgroup. In the prefusion state, the RSV fusion protein (F) is a major target of neutralizing antibodies, serving as the basis of Pfizer’s RSV vaccine. Variations in the F protein sequence among RSV-A and RSV-B subgroups are clustered in a key antigenic site, a target for potent neutralizing antibodies

Adults with underlying chronic conditions, including asthma, diabetes, and chronic obstructive pulmonary disease, constitute a vulnerable population prone to RSV-associated LRTD. Despite the substantial risk, to date, there are no approved RSV vaccines for adults aged 18 to 59. GSK’s AREXVY and Pfizer’s ABRYSVO have been licensed by FDA and recommended by CDC for adults ages 60 and older, using shared clinical decision-making. Pfizer currently is the only company with an RSV vaccine to help protect older adults as well as infants through maternal immunization. Pfizer’s MONeT study, therefore, assumes paramount importance in addressing this unmet medical need by assessing the immunogenicity and safety of ABRYSVO in the 18 to 59 years old demographic.

Pfizer’s ABRYSVO Met Co-primary Immunogenicity Endpoints and Primary Safety Endpoint in Phase 3 MONeT Study

The trial successfully met its co-primary immunogenicity endpoints and primary safety endpoint:

  • Participants demonstrated non-inferior RSV-A and RSV-B subgroup neutralizing responses compared to the Phase 3 RENOIR study involving over 34,000 adults aged 60 or older, where vaccine efficacy was previously demonstrated.
  • Participants exhibited at least a four-fold increase in serum neutralizing titers for RSV-A and RSV-B one month post-ABRYSVO administration compared to pre-vaccination levels.
  • ABRYSVO was well-tolerated throughout the trial, with safety findings consistent with prior investigations across diverse populations.

Additionally, Pfizer achieved its diversity recruitment objectives for the study, ensuring robust representation from various demographic groups.

Leveraging immunobridging studies to extrapolate efficacy from older to younger adults presents a well-established regulatory pathway. Furthermore, the company intends to disseminate these findings through peer-reviewed publication and scientific conferences.

Dr. Annaliesa Anderson, Senior Vice President and Head of Vaccine Research and Development at Pfizer, expressed optimism about the results, underscoring the potential of ABRYSVO to mitigate RSV-associated illness in at-risk adults, pending regulatory approval, stating:

“These encouraging results provide evidence that ABRYSVO can help protect adults with increased risk against RSV-associated illness. 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.”

The MONeT trial (NCT05842967) is a Phase 3, multicenter study investigating the safety, tolerability, and immunogenicity of ABRYSVO in adults vulnerable to RSV-associated disease, including those with chronic medical conditions and immunocompromised individuals.

RSV is a contagious virus known to cause respiratory illness, particularly severe in young infants, older adults, and individuals with certain chronic medical conditions. Pfizer’s ABRYSVO is a bivalent vaccine designed to confer broad protection against all RSV-LRTD, targeting the prefusion state of the RSV fusion protein (F) as the primary neutralizing antibody target.

Following FDA approval in May 2023 for individuals aged 60 and older and subsequent endorsements by the ACIP, Pfizer’s ABRYSVO has garnered approvals across various regions, including the EU, Argentina, the UK, Canada, Macau, Japan, and Australia, for both older adults and maternal immunization to protect infants.

ABRYSVO is currently indicated in the US for the prevention of lower respiratory tract disease (LRTD) caused by RSV in people aged 60 and older, as well as for pregnant individuals at 32 through 36 weeks gestational age to prevent LRTD and severe LRTD caused by RSV in infants from birth through 6 months of age.

About the MONeT Phase 3 Clinical Trial

MONeT, an acronym for the RSV IMmunizatiON Study for AdulTs at Higher Risk of Severe Illness, is a Phase 3, multicenter clinical trial registered under NCT05842967. It aims to evaluate the safety, tolerability, and immunogenicity of ABRYSVO in adults susceptible to RSV-associated disease. The study encompasses two subgroups: Substudy A focuses on adults with specific chronic medical conditions, while Substudy B targets immunocompromised adults.

Substudy A employs a double-blinded approach, randomizing 681 adults aged 18 to 59 with chronic conditions. Participants are assigned in a 2:1 ratio to receive either a single dose of ABRYSVO or a placebo. On the other hand, Substudy B adopts an open-label design and involves approximately 200 immunocompromised adults aged 18 or older. Among these participants, nearly half are aged 60 or older, and they receive two doses of ABRYSVO administered one month apart.

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