UNITED KINGDOM — Sanofi and AstraZeneca have announced promising results from the Phase IIIb HARMONIE trial, revealing that their respiratory syncytial virus (RSV) antibody candidate, nirsevimab, provides robust protection for infants under 12 months of age.

The trial demonstrated that a single dose of nirsevimab led to an 83.21% reduction in hospitalizations related to lower respiratory tract disease (LRTD) associated with RSV infections when compared to no immunization.

Additionally, admissions due to severe RSV-related LRTD, characterized by oxygen levels below 90%, decreased by 75.71% following administration of nirsevimab.

Furthermore, the overall incidence of all-cause LRTD hospitalization was lowered by 58.04% with nirsevimab, which could potentially alleviate the burden on healthcare systems if all infants receive the antibody treatment, according to the companies’ press release.

The HARMONIE trial, which enrolled approximately 22,000 infants, is a large-scale study conducted in Europe to evaluate the efficacy of a single dose of nirsevimab in providing protection against RSV compared to no immunization.

In addition to efficacy, the trial also assessed the safety profile of nirsevimab and found it to be favorable and consistent with previous findings.

Nirsevimab is an investigational long-acting antibody that works by binding to the part of the RSV virus used to attach to its target cells, thus preventing infection at the cellular level.

In January 2023, the US Food and Drug Administration (FDA) accepted the Biologics License Application (BLA) for nirsevimab, which was supported by data from the Phase III MELODY and Phase II/III MEDLEY trials, as well as other Phase IIb data.

Throughout these studies, a single dose of nirsevimab consistently demonstrated protection levels of approximately 80% against medically attended RSV infections.

Sanofi and AstraZeneca initiated their partnership for the development and commercialization of nirsevimab in March 2017.

Intensifying competition in RSV vaccines

The release of positive data by Sanofi and AstraZeneca coincides with the upcoming meeting of the Vaccines and Related Biological Products Advisory Committee (VRBPAC) to discuss Pfizer’s RSV vaccine candidate, Abrysvo.

Pfizer is proposing Abrysvo as a maternal injection to prevent RSV infections in infants from birth through 6 months of age. The VRBPAC meeting is scheduled for May 18.

Pfizer is one of the frontrunners in the race to develop a pediatric RSV vaccine.

Preliminary data from the Phase III MATISSE trial, which was used to support Abrysvo’s BLA, demonstrated a vaccine efficacy rate of 66.7% against RSV-associated lower respiratory tract illness (LRTI) with two or more symptoms.

The efficacy rate increased to 85.7% against severe LRTI, which included at least three symptoms.

The FDA is expected to make a decision regarding Abrysvo’s approval in the pediatric setting by August 2023.

Previously, GSK was also a key player in the development of an RSV vaccine for children. However, in February 2020, the company had to halt three maternal trials due to safety concerns.

One trial has been completely withdrawn, while the other two remain active but have discontinued vaccination.

Last week, GSK received FDA approval for the first RSV vaccine for older adults aged 60 years and above.

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