# Immunogenicity and Safety Following 1 Dose of AS01E-Adjuvanted Respiratory Syncytial Virus Prefusion F Protein Vaccine in Older Adults: A Phase 3 Trial

## TL;DR

A single dose of an RSV vaccine in older adults triggered strong immune responses that lasted over a year and was safe.

## Contribution

Demonstrates long-term immune persistence and safety of a single-dose RSV vaccine in older adults.

## Key findings

- RSV-specific neutralization titers remained elevated for at least 1 year post-vaccination.
- The vaccine was well tolerated with mostly mild to moderate adverse events.
- Cell-mediated and humoral immune responses declined over time but stayed above pre-vaccination levels.

## Abstract

The recently approved AS01E-adjuvanted respiratory syncytial virus (RSV) prefusion F protein–based vaccine for older adults (RSVPreF3 OA) demonstrated high efficacy against RSV-related disease in ≥60-year-olds.

This ongoing phase 3 study in ≥60-year-olds evaluates immune persistence until 3 years after RSVPreF3 OA vaccination. Here, we describe interim results on humoral and cell-mediated immunogenicity, reactogenicity, and safety until 1 year post–dose 1.

In total, 1653 participants were vaccinated. One month post–dose 1, neutralization titers increased 10.5-fold (RSV-A) and 7.8-fold (RSV-B) vs pre–dose 1. Titers then declined to levels 4.4-fold (RSV-A) and 3.5-fold (RSV-B) above pre–dose 1 at month 6 and remained 3.1-fold (RSV-A) and 2.3-fold (RSV-B) above pre–dose 1 levels after 1 year. RSVPreF3-binding immunoglobulin G levels and CD4+ T-cell frequencies showed similar kinetics. Solicited administration-site and systemic adverse events (mostly mild to moderate and transient) were reported by 62.2% and 49.5% of participants. Serious adverse events were reported by 3.9% of participants within 6 months post–dose 1; 1 case was considered vaccine related.

One RSVPreF3 OA dose elicited cell-mediated and RSV-A– and RSV-B–specific humoral immune responses that declined over time but remained above pre–dose 1 levels for at least 1 year. The vaccine was well tolerated with an acceptable safety profile.

Clinical Trials Registration.
NCT04732871 (ClinicalTrials.gov).

One dose of prefusion F protein–based vaccine for older adults administered to ≥60-year-olds induced humoral and cell-mediated immune responses that remained above pre–dose 1 levels for at least 1 year. The vaccine was well tolerated with an acceptable safety profile.