Cocrystal Pharma Advances First Oral Norovirus Antiviral CDI-988 into Phase 1b Human Challenge Study
Key Insights
Cocrystal Pharma received IRB approval from Emory University School of Medicine to initiate a Phase 1b human challenge study with CDI-988, the first oral antiviral drug candidate for norovirus (search) prevention and treatment.
The randomized, double-blind, placebo-controlled study will enroll up to 40 healthy subjects ages 18-49 and evaluate CDI-988's efficacy in reducing clinical symptoms and viral shedding.
CDI-988 targets the highly conserved 3CL protease (search) region across all norovirus (search) strains and addresses a significant unmet medical need, as no approved treatments or vaccines currently exist for norovirus infections.
Cocrystal Pharma has received Institutional Review Board (IRB) approval from Emory University School of Medicine to initiate a Phase 1b human challenge study with CDI-988, marking a significant milestone for the first oral antiviral drug candidate developed for norovirus (search) prevention and treatment. Subject enrollment is expected to begin in the first quarter of 2026, following FDA clearance of the company's investigational New Drug (IND) application.
The approval addresses a critical unmet medical need, as there are currently no approved treatments or vaccines available for norovirus (search) infection, despite the virus causing an estimated 700 million cases worldwide each year.
Novel Mechanism Targets Conserved Viral Region
CDI-988 was specifically designed as a broad-spectrum inhibitor targeting a highly conserved region of the viral 3CL protease (search) across all noroviruses, including GII.4 and recently re-emerging GII.17 strains. The drug candidate was developed using Cocrystal's proprietary structure-based drug discovery platform technology, which provides three-dimensional structures of inhibitor complexes at near-atomic resolution.
"CDI-988 may revolutionize the management of the highly contagious norovirus (search), which is known for quickly spreading in hospitals, nursing homes, cruise ships, schools, disaster relief sites, military settings and other semi-closed environments," said James Martin, CFO and co-CEO of Cocrystal Pharma. "Used as a prophylaxis, oral CDI-988 could offer a potential solution and add a new layer of defense."
Phase 1b Study Design and Endpoints
The randomized, double-blind, placebo-controlled Phase 1b study will be conducted at Emory University and involve up to 40 healthy subjects ages 18-49. Participants will be screened and infected with the norovirus (search) GII.2 (Snow Mountain Virus) strain.
The study's primary efficacy endpoint focuses on assessing the reduction in incidence of clinical symptoms, while the secondary efficacy endpoint evaluates the reduction in viral shedding and disease severity. The study will also assess the safety and pharmacokinetic profile of CDI-988.
"This approval from the Emory IRB marks a significant milestone in advancing our Phase 1b norovirus (search) challenge study," said Sam Lee, Ph.D., Cocrystal's President and co-CEO. "We are very excited about collaborating with the Emory team, given their exceptional expertise in norovirus and experience in human challenge studies."
Substantial Disease Burden and Economic Impact
Norovirus (search) represents a significant global health challenge, causing symptoms of acute gastroenteritis (search) including nausea, vomiting, stomach pain and diarrhea, as well as fatigue, fever and dehydration. The infection spreads rapidly in semi-closed and crowded settings, making outbreaks especially difficult to control.
The virus causes an estimated 200,000 deaths worldwide each year, with a societal cost of approximately $60 billion. In the United States, norovirus (search) is responsible for about 21 million cases of acute gastroenteritis (search) annually, including 109,000 hospitalizations, 465,000 emergency department visits and nearly 900 deaths, with an estimated annual economic burden of $10.6 billion.
Promising Safety Profile and Future Presentations
In August 2025, Cocrystal announced favorable Phase 1 safety and tolerability data from all CDI-988 dose cohorts, including the highest dose of 1200 mg. The company received a Study May Proceed Letter from the FDA for the Phase 1b challenge study in September 2025.
The company plans to present initial progress from the norovirus (search) challenge study at the 39th International Conference on Antiviral Research (ICAR2026) in Prague, Czech Republic, scheduled for April 27–May 1, 2026. Dr. Lee will discuss the ongoing Phase 1b challenge study and CDI-988's potential as both a prophylactic and therapeutic option for norovirus infection.
Based on its novel mechanism of action and broad-spectrum antiviral activity, CDI-988 also represents a potential oral treatment for both noroviruses and coronaviruses, positioning it as a pan-viral protease (search) inhibitor with applications beyond norovirus (search) infections.