A first-in-human Phase 1/1b randomized trial evaluating the safety and immunogenicity of a respiratory syncytial virus (RSV) virus-like particle subunit vaccine (IVX-121) in healthy young and older adults.

In 30 seconds

This randomized Phase 1/1b trial evaluated the safety and immunogenicity of IVX-121, an investigational RSV virus-like particle vaccine, in 90 healthy adults aged 18–45 years and 130 aged 60–75 years. Participants received a single intramuscular dose at one of three dose levels, with or without aluminum hydroxide, or placebo; outcomes were assessed through Day 180, with an older-adult extension. Adverse reactions were generally mild, with no vaccine-related serious adverse events. All doses and formulations boosted preexisting RSV neutralizing antibodies, which remained above baseline for at least 6 months.

Key findings

• Adverse reactions were generally mild, and no vaccine-related serious adverse events were reported.
• All dose levels and formulations boosted preexisting neutralizing antibody responses against RSV A and B, remaining above baseline for at least 6 months.
• There was no clear dose response, and aluminum hydroxide did not appear to improve immunogenicity; the trial was not statistically powered for treatment-group comparisons.
• A second dose in older adults modestly increased RSV A neutralizing antibodies but did not increase RSV B responses.

Why it matters

RSV causes substantial lower respiratory tract disease, including in older adults. These early-stage findings provide evidence that IVX-121 can induce antibody responses in both younger and older healthy adults, while showing no vaccine-related serious adverse events in the trial. The results inform further evaluation of the vaccine but do not establish its ability to prevent RSV illness.

What to keep in mind

This Phase 1/1b trial was not statistically powered to compare treatment groups, and it assessed safety and immunogenicity rather than clinical protection against RSV disease.