Pfizer Abrysvo RSV Vaccine Meets Primary Endpoints for Adults Ages 18 to 59

This morning, Pfizer announced results from its phase 3 MONeT (RSV IMmunizatiON Study for AdulTs at Higher Risk of Severe Illness, trial which is evaluating a single dose of its respiratory syncytial virus (RSV) vaccine, RSVPreF3 (Abrysvo), vs placebo in adults 18 to 59 years of age at risk of developing severe RSV-associated lower respiratory tract disease (LRTD).¹

This multicenter, clinical trial has been investigating the safety, tolerability, and immunogenicity of the Pfizer vaccine. For the trial, they created 2 cohorts: (substudy RSV-A) which includes adults with certain chronic medical conditions; and (substudy RSV-B) which includes adults who are immunocompromised.¹

Substudy RSV-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 RSVPreF3 or placebo. Substudy RSV-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 2 doses of RSVPreF3, 1 month apart.¹

The results from the MONeT study showed the vaccine achieved its co-primary immunogenicity endpoints and primary safety endpoint according to Pfizer and some of the results include:

• Participants in RSV-A and RSV-B subgroup demonstrated neutralizing responses non-inferior to the response seen in the phase 3 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 4-fold increase in serum neutralizing titers for RSV-A and RSV-B 1 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.¹

“These encouraging results provide evidence that Abrysvo can help protect adults with increased risk against RSV-associated illness,” said Annaliesa Anderson, PhD, senior vice president and head, Vaccine Research and Development, Pfizer. ¹

During the pandemic, people with immunocompromised systems and chronic conditions had a greater risk of severe COVID-19 disease and mortality. For those aforementioned patient groups, Pfizer sees an unmet need to offer a prophylactic modality for RSV.

“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,” Anderson stated.¹

Previous FDA Approvals
If approval is gained for the 18 to 59 age group, the Pfizer vaccine would have the farthest-reaching coverage for people in protecting against RSV.

Last year, Pfizer had gained 1 FDA approval for the vaccine for infants from birth to 6 months.The FDA’s decision was based on data from the pivotal, randomized, double-blind, placebo-controlled phase 3 clinical trial MATISSE, which evaluated efficacy, safety, and immunogenicity of the vaccine against LRTD and severe LRTD due to RSV in infants born to healthy individuals who were vaccinated during pregnancy. The trial, which was conducted in 18 countries over 4 RSV seasons, followed infants for up to 2 years.²

Overall, 3682 maternal participants aged 49 years or younger, at 24-36 weeks’ gestation on the day of planned RSVpreF injection, received a single intramuscular injection of 120 μg of RSVpreF vaccine and 3676 received placebo, with investigators subsequently evaluating 3570 and 3558 infants, respectively.²

And another FDA approval for the vaccine was for seniors 60 years of age and older. This approval allows the use of Abrysvo in individuals aged 60 years and older to prevent lower respiratory tract disease caused by RSV.³

The FDA's decision to approve Abrysvo for seniors from data obtained from the phase 3 clinical trial known as RENOIR (RSV vaccine Efficacy study iNOlder adults Immunized against RSV disease). RENOIR is a global, randomized, double-blind, placebo-controlled study designed to evaluate the efficacy, immunogenicity, and safety of a single dose of the vaccine in adults aged 60 and older.³

Nearly 37,000 participants were enrolled in RENOIR, with half receiving RSVpreF 120 μg and the other half receiving placebo in a 1:1 ratio.³

According to the company, 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.¹

References
1. 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 Press release. 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.Bigica A. FDA Approves Pfizer's Maternal RSV Vaccine Abrysvo to Protect Infants. August 21, 2023. Accessed April 9, 2024. FDA Approves Pfizer's Maternal RSV Vaccine Abrysvo to Protect Infants https://www.contagionlive.com/view/fda-approves-pfizer-maternal-rsv-vaccine-rsvpref-abrysvo-to-protect-infants

3. Cosdon N. A Milestone in RSV Prevention: FDA Approves Pfizer's Abrysvo Vaccine for Older Adults. June 1, 2023 Accessed April 9, 2024.
https://www.contagionlive.com/view/a-milestone-in-rsv-prevention-fda-approves-pfizer-s-abrysvo-vaccine-for-older-adults