Pfizer: MONeT Study Topline Data Positive for Abrysvo in Adults Aged 18 to 59 Years at High Risk for RSV-LRTD

The ongoing phase 3 MONeT trial of adults aged 18 to 59 years at increased risk for respiratory syncytial virus-associated lower respiratory tract disease (RSV-LRTD) who received Abrysvo met its coprimary endpoints for immunogenicity as well as the primary safety endpoint, according to Pfizer.¹

In the announcement of the top-line results, made Tuesday morning, Pfizer said the vaccine was well-tolerated in the vulnerable population studied and that participants in both RSV-A and RSV-B subgroups demonstrated neutralizing responses that were non-inferior to the response seen in the Phase 3 RENOIR study of Abrysvo. RENOIR enrolled more than 34 000 adults aged 60 years and older and comprised the data on which the US Food and Drug Administration approved Abrysvo in June 2023 with an indication for RSV-LRTD prevention in the adult population over age 60 years.

MONeT participants also achieved at least a 4-fold increase in serum neutralizing titers for RSV-A and RSV-B 1 month after receipt of Abrysvo vs pre-vaccination.

Pfizer plans to submit the pivotal MONeT trial findings to regulatory agencies pursuing approval of an expanded label for Abrysvo to include those as young as 18 years of age and older.

The increased risk of hospitalization for RSV-LRTD among individuals with underlying chronic conditions is high among US adults aged 50 to 64 years, at nearly 25%, but is not insignificant in the younger population either where close to 10% are at risk of severe disease.² The US Food and Drug Administration in 2023 approved 2 vaccines against RSV for US adults aged 60 years and older but there has yet to be an application submitted for the 18 to 59 set. Pfizer looks to fill this unmet need.

“These encouraging results provide evidence that Abrysvo can help protect adults with increased risk against RSV-associated illness,” Annaliesa Anderson, PhD, senior vice president and head, vaccine research and development at Pfizer said in the company statement. “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.”¹

The phase 3 multicenter MONeT study is investigating the safety, tolerability, and immunogenicity of a single dose of Abrysvo in adults aged 18 to 59 years with chronic medical conditions, eg, asthma, diabetes, and chronic obstructive pulmonary disease (substudy A) and those who are immunocompromised (substudy B), according to Pfizer.¹ In the double blind substudy A 681 participants were randomly assigned in a 2:1 ratio to receive a single dose of Abrysvo or placebo. Substudy B is an open label study that enrolled approximately 200 immunocompromised adults aged 18 years or older, “roughly half of which” were aged 60 years or older. This group received 2 doses of Abrysvo 1 month apart.

Pfizer stated in its announcement that data from the study reflect the company's diversity commitment, mirroring the broader US population. The cohort also comprised a balanced distribution of underlying medical conditions.

Importantly the company points to the use of immunobridging studies to extrapolate efficacy from older to younger adults as established regulatory pathway.¹

Pfizer also indicated it will publish the MONeT findings in a peer-reviewed scientific journal and share the full set of data at an upcoming scientific conference.

References

1. Pfizer announces positive top-line results from phase 3 study of Abrysvo in adults aged 18 to 59 at increased risk of RSV disease. News release. Pfizer. April 9, 2024. Accessed April 9, 2024. https://www.pfizer.com/news/press-release/press-release-detail/pfizer-announces-positive-top-line-results-phase-3-study-1
2. Weycker D, Averin A, Houde L, et al. Rates of lower respiratory tract illness in US adults by age and comorbidity profile. Infect Dis Ther. 2024;13:207–220. doi: 10.1007/s40121-023-00904-z.