NCT06279871

Immunogenicity and Safety Study of Self-amplifying mRNA COVID-19 Vaccine Administered With Influenza Vaccines in Adults

A Phase 3, Multicenter, Observer-blind, Randomized, Controlled Study to Evaluate the Immunogenicity, Reactogenicity, and Safety of a Self-Amplifying RNA COVID-19 Vaccine (ARCT-2303), Administered Concomitantly With Quadrivalent Influenza Vaccines, in Adults

• Status: Completed
• Phase: Phase 3
• Study type: Interventional
• Enrollment: 1,514 (actual)
• Sponsor: Arcturus Therapeutics, Inc. · Industry
• Sex: All
• Age: 18 Years
• Healthy volunteers: Accepted

Summary

This is a multicenter, observer-blind, randomized, controlled phase 3 study to evaluate the immunogenicity, reactogenicity, and safety of an investigational self-amplifying RNA COVID-19 vaccine (ARCT-2303) administered concomitantly with quadrivalent influenza vaccines or standalone in adults who previously received authorized COVID-19 vaccine.

Detailed description

Approximately 1680 participants previously vaccinated with authorized COVID-19 vaccine will be enrolled in this study in two age cohorts (younger adults and older adults). Within each cohort, participants will be randomly assigned in a ratio of 1:1:1 to receive the ARCT-2303 vaccine concomitantly with a quadrivalent influenza vaccine, the ARCT-2303 vaccine and placebo, or the quadrivalent influenza vaccine and placebo. The assessment of immunogenicity will be performed 28 days after vaccination. To provide equal benefit from the participation in the study and complete seasonal vaccination against COVID-19 and influenza, a switchover vaccine dose (influenza, ARCT-2303 or placebo) will be administered 28 days after initial vaccination. All participants will be followed up for safety assessment until the end of the study. A historical control group vaccinated on a similar schedule (ARCT-154 vaccine) from a previous study (ARCT-154-J01) will be used to compare with the immunogenicity of the ARCT-2303 vaccine. Cohort A (younger adults; approximately 1200 participants): * Group 1a (ARCT-2303/Influenza vaccine): participants will receive one dose of ARCT-2303 and one dose of Influenza vaccine (opposite arms) on Day 1, and one dose of placebo on Day 29. * Group 2a (ARCT-2303): participants will receive one dose of ARCT-2303 and one dose of placebo (opposite arms) on Day 1, and one dose of Influenza vaccine on Day 29. * Group 3a (Influenza vaccine): participants will receive one dose of Influenza vaccine and one dose of placebo (opposite arms) on Day 1, and one dose of ARCT-2303 on Day 29. Cohort B (older adults; approximately 480 participants): * Group 1b (ARCT-2303/Influenza vaccine): participants will receive one dose of ARCT-2303 and one dose of Influenza vaccine (opposite arms) on Day 1, and one dose of placebo on Day 29. * Group 2b (ARCT-2303): participants will receive one dose of ARCT-2303 and one dose of placebo (opposite arms) on Day 1, and one dose of Influenza vaccine on Day 29. * Group 3b (Influenza vaccine): participants will receive one dose of Influenza vaccine and one dose of placebo (opposite arms) on Day 1, and one dose of ARCT-2303 on Day 29.

Conditions

• COVID-19

Interventions

Type	Name	Description
BIOLOGICAL	ARCT-2303	Self-Amplifying RNA COVID-19 vaccine (Omicron XBB.1.5)
BIOLOGICAL	Influenza vaccine	Licensed cell-based influenza vaccine
BIOLOGICAL	Influenza vaccine, adjuvanted	Licensed influenza vaccine, adjuvanted
OTHER	Placebo	0.9% saline

Timeline

• Start date: 2024-03-27
• Primary completion: 2024-10-09
• Completion: 2024-11-21
• First posted: 2024-02-28
• Last updated: 2025-12-12
• Results posted: 2025-12-12

Locations

29 sites across 4 countries: Australia, Costa Rica, Honduras, Philippines

Regulatory

• FDA-regulated drug study