Cellid announced on the 26th through a regulatory filing that its COVID-19 vaccine candidate 'AdCLD-CoV19-1 OMI' failed to demonstrate non-inferiority, the primary immunogenicity endpoint, in a global Phase 3 clinical trial. However, no serious adverse drug reactions were reported following vaccination with the test vaccine, and it was confirmed to meet the expected safety profile.

Clinical Trial Overview This Phase 3 clinical trial was conducted to evaluate the immunogenicity and safety of a COVID-19 vaccine booster in 4,000 adults aged 19 and older. The trial was designed as a multi-country, multi-center, observer-blinded, randomized, active-controlled study, with the test group receiving 'AdCLD-CoV19-1 OMI' and the active control group receiving Pfizer's 'Comirnaty.' The clinical trial period is from November 27, 2023, to November 22, 2025.

Primary Immunogenicity Evaluation Results At 28 days post-vaccination, the adjusted Geometric Mean Titer (GMT) was 15,397.26 in the test group and 37,091.72 in the control group. The adjusted GMT ratio was 0.42 (95% confidence interval 0.38–0.45), which failed to meet the non-inferiority margin of 0.67 set in the clinical trial protocol, thus failing to demonstrate non-inferiority compared to the control group.

Additionally, the Seroresponse Rate (SRR) was 17.12% (139/812) in the test group and 42.64% (171/401) in the control group. The difference between the two groups was -25.51% (95% confidence interval -30.96% to -20.05%), which falls short of the non-inferiority margin of -10%.

Safety Evaluation and Future Plans In contrast to the disappointing immunogenicity results, positive findings were confirmed for safety. During the primary study period, there were no serious adverse drug reactions following vaccination with the test vaccine. The overall incidence of serious adverse events (SAEs) was 5 cases (0.17%) in the test group, 2 cases (0.43%) in the active control group, and 2 cases (0.37%) in the placebo control group. The company explained that follow-up observation results up to 52 weeks post-vaccination also showed no new safety concerns.

Cellid plans to continue the development of its COVID-19 vaccine based on the safety data obtained from this trial. The company is currently reviewing additional clinical trial designs and development strategies from multiple angles to supplement the immunogenicity results, and specific future plans will be disclosed during a shareholder meeting in July after completing an internal review.