Shares of Icosavax (NASDAQ: ICVX) jumped 58% on Wednesday after the company provided a six-month update on results of its Phase 1/1b trial of IVX-121 against Respiratory Syncytial Virus (RSV).

Icosavax says data showed that the drug was able to maintain a sustained neutralizing antibody response against RSV for at least six months after a single administration.

The update was based on the company's virus-like particle (VLP) platform technology, which the company says it is using to develop vaccines against infectious diseases, with an initial focus on respiratory diseases.

Results of the Phase 1/1b trial of IVX-121 showed that the drug continued to be well-tolerated with no safety concerns and no vaccine-related serious adverse events.

The company says that the data demonstrated ongoing neutralizing antibody responses to a single administration of IVX-121 at three dosage levels (25, 75, and 250 µg) in the groups without adjuvant. Samples were taken at baseline, day 28, and day 180, and neutralizing antibodies were measured in international units per milliliter (IU/mL) using the World Health Organization's international reference standard.

The durability of IVX-121 was found to be comparable in both young and older adult groups in the day 180 immunogenicity data. In the older adult group, geometric mean titers for RSV-A neutralizing antibodies that were previously reported at up to 7,561 IU/mL at day 28 were observed to persist at up to 6,184 IU/mL through day 180.

These titers were maintained within a range of 64-98% relative to the previously reported values at day 28. Geometric mean titers for RSV-B showed greater variability but were still maintained above baseline through day 180.

Icosavax plans to provide a 12-month immunogenicity update from an extension of this Phase 1b trial in mid-2023, and intends to present additional data from the trial at a future medical meeting.

Shares of Icosavax trade on the NASDAQ under the ticker symbol ICVX. For more information visit www.icosavax.com.