Icosavax, Inc. announced the initiation of a Phase 1 clinical trial of IVX-A12, a combination bivalent RSV and hMPV VLP vaccine candidate, in older adults. IVX-A12 is comprised of IVX-121, Icosavax's RSV prefusion F protein VLP vaccine candidate, and IVX-241, Icosavax's hMPV prefusion F protein VLP vaccine candidate. The company previously announced positive topline interim Phase 1/1b results for IVX-121 in June 2022.

With this trial initiation, IVX-A12 becomes the first combination bivalent vaccine candidate against both respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) to enter the clinic, and the first candidate from Icosavax's novel VLP platform to receive IND authorization in the U.S. IVX-A12 Phase 1 Trial Design: The Phase 1 clinical trial of IVX-A12 is a randomized, observer-blinded, placebo-controlled, multi-center study designed to evaluate the safety and immunogenicity of multiple dosage levels of IVX-A12, with and without CSL Seqirus' proprietary adjuvant MF59®. The company anticipates enrolling up to 120 healthy older adults aged 60 to 75 years. Subjects will be administered a single shot of IVX-A12, at one of three combination dosage levels below, or placebo: 75 µg of IVX-121 and 75 µg of IVX-241, with or without MF59®; 75 µg of IVX-121 and 150 µg of IVX-241, with or without MF59®; 75 µg of IVX-121 and 225 µg of IVX-241, without MF59®.

The objective of the Phase 1 study of IVX-A12 is to evaluate safety, and immunogenicity against both RSV and hMPV, as well as to assess immunologic non-interference. Icosavax anticipates announcing topline interim results from this Phase 1 trial in mid-2023, with subjects thereafter followed through 12 months after vaccination. Contingent upon a positive outcome from this trial, the company then expects to initiate a Phase 2 trial for IVX-A12 in 2H 2023.

The IVX-121 (RSV) component of IVX-A12 (RSV/hMPV) demonstrated robust immunogenicity and favorable tolerability in a prior Phase 1/1b study, and a subset of these Phase 1b older adult subjects continue to be followed, with six-month immunogenicity data expected by early-2023 and 12-month immunogenicity data in mid-2023.